Hi Byte,
Welcome to YamahaSynth! Thanks for the ‘question’.

Here is what is going on. The FC7 does not address the internal tone generator with MIDI. Rather it addresses the internal tone engine directly, much like the keys of the keyboard do. What any controller sends Out via MIDI is totally separate from what it may be assigned to do internally.

The second most important function that the Foot Controller can be assigned to is not on your list.
Foot Control - CC04

The MX-series is the entry level synth in the Yamaha synthesizer lineup and has but one Foot Controller jack, and a Sustain jack. The default for the Foot Controller is CC11 Expression (quite naturally) This is, by far the most requested function for an FC7 sweep type pedal. The pedal jacks can be assigned to function differently in UTILITY mode.

The default for the FC7 jack EXPRESSION (CC11) — cc11 is a fixed function - it will always control the musical performing volume. Where CC7 Main Volume can be understood as the Channel’s Volume, like on a mixing console; Expression CC11 is like the volume control on the musical instrument. It works within the maximum range as set by the mixer’s channel setting.

The other standard assignment for the FOOT CONTROLLER is CC04, called ‘Foot Control”; this does not have a specific thing that it controls. Much like the MW CC01, you must assign it to do something, on a program-by-program basis. Much like the MW might be pitch modulation depth (vibrato) on a synth lead, it might be Rotary Speaker Speed on an organ sound, it might be opening the filter on a synth pad sound, or even fading in strings behind a piano in another program. The CC04 Foot Control can do all the same things.

Foot Control is a standard CC# reserved for use with a sweep type foot pedal. You can program it to do things on a program-by-program basis. It might be used as Element Level (within a single sound - say Elements 1, 2, 3, and 4 are reproducing an acoustic piano sound, and Elements 5, 6, 7, and 8 are reproducing a string orchestra sound... Foot Control can be assigned to control just specific Elements — allowing you fade the strings in and out with your pedal. You can see how Expression, and Main Volume would cause all the Elements to change; Foot Control can be assigned internally to adjust just the Elements you desire.

Foot Control can be a very surgical output level control, but in another program can be assigned be the Wah-Wah pedal for a Clavinet or Guitar.
Foot Control could be used to Pan just specific Elements within a Part.
Foot Control can be assigned directly to Cutoff
Foot Control can be assigned directly to Resonance.
Foot Control can assigned directly to the Attack of the AEG
Foot Control can be assigned directly to the Release of the AEG
Foot Control can be assigned directly to the Decay portion of the AEG
Foot Control can be assigned directly to control the Rev Send
Foot Control can be assigned directly to control the Chorus Send

As we mentioned, the MX does not use the CC# to address itself. When you have assigned the Foot Controller to cc4, you get to choose what it controls directly in the synthesizer. And no matter what you choose (as you see, all of the functions you have listed are there — plus a whole lot more!) what goes out via MIDI is cc4.

Please see the CONTROL LIST “Controller Set Destination” listing, in the Data List booklet, page 52 for all the Assignable functions.. all are available for Foot Control CC04.

When you record the movement of the pedal as MIDI data to a sequencer, then play it back to this Voice... I will respond exactly as programmed ... be it Element Level, Reverb Send, Filter Cutoff, whatever.

Hope this helps - it is not a bug but in fact is the way most gear works. MIDI is an add on... Not the language a product addresses itself... MIDI is the language that all product (even those from other manufacturers gear can understand).

Your MX has 8 oscillators (Elements) per Voice, that is not an industry standard (trust me). So being able to control each of them, individually, via MIDI, requires an *assignable* cc, like cc4, that can be directed to where your MX can use it. The cc4 message is directed to the parameter it is programmed to control. MIDI is not the language that the synth speaks to itself. But when it receives the message via MIDI, it ‘knows’ what to do.

It is very much like how your brain works your body... it has a direct message that says, move your arm. You do not have to use language to do it. But when someone asks you to move your arm, you know just what to do. MIDI represents the idea put into a language... but when the synth is addressing itself — it just goes ahead and does it. Much like your brain and the muscles in your arm. (Think of this as a system exclusive message)! lol

If... as I assume you have been experimenting ... if you set the FC to send CC74 expecting the synth’s filters to move... they will not.
CC74 will address the filters if and when that message arrives via MIDI. There are two pathways — one very direct, the other is MIDI.
Same as there is directly pressing the keys to play the tone generator, and there are MIDI messages that arrive to play the tone generator.

Because... the Synth does not address itself with CC messages — rather it generates these messages expressly to Transmit Out via MIDI when you physically engage a control. This is how cc4 coming in via MIDI will be able to control level, Rev send, Chorus Send, Pan some thing, be a wah pedal, change rotary speaker speed, slow the attack, etc., etc., etc. once it arrives, the synth’s architecture determines what happens.

OK, this is very comprehensive answer and it will be a lot for me to digest.
I feel though maybe I've complicated the things too much, and it's hard to sort things out now.
So let's simplify the scenario: we leave out Chorus/Reverb send, filter controls and the envelope generator, and only test two very basic cases:

1) FC1 = 07[Volume ]
- sending Volume control messages (CC7) from an external controller: works, volume is changed
- sending Panning control messages (CC10) from an external controller: works, panning is changed
- using the pedal controller: works, volume is changed

So far so good.

2) FC1 = 10[Pan ]
- sending Volume control messages (CC7) from an external controller: still works, volume is changed
- sending Panning control messages (CC10) from an external controller: DOES NOT work anymore, panning is NOT changed. What gives...?
- using the pedal controller: nothing happens. Why is that...?

So volume always works just fine, but controlling Panning with the FC1 input proves to be impossible.
How can this asymmetrical behaviour be explained?

I've torn the manuals upside down and I cannot find any clue to explain why Volume always works (via either FC1 or external MIDI) but Panning never works via FC1, and it only works via MIDII if FC1 is NOT assigned to CC10.

If I am to play "which one doesn't belong" - I notice that the parameters when the FC1 pedal is able to "share" as the controller for a given CC standard function - that CC said CC is modulated by a physical controller (it's setup to "look" at controllers). The ones that do not respond are those that are parameters that are not tied to standard controllers (like mod, ribbon, etc). The ones that "don't work" are not normally attached to controllers but instead only respond to external MIDI messages.

Well not really.
Panning, EG Attack/Decay/Sustain/Release, Filter Cutoff/Resonance, Chorus Send and Reverb Send are attached to physical controllers and still do not work.

The second most important function that the Foot Controller can be assigned to is not on your list.
Foot Control - CC04
.............
Please see the CONTROL LIST “Controller Set Destination” listing, in the Data List booklet, page 52 for all the Assignable functions.. all are available for Foot Control CC04.

Why would this be important if the engine doesn't care at all on which CC number is assigned to it? Its is just like you mentioned.

For the Voice Control Set, the CC number is entirely irrelevant, and only the FC1 "controller" per se acts as Source for the (pag 52) Destinations.
FC1 It can be linked to ANY CC number ("Foot Control CC04" has nothing special to it), and it will STILL work the same with respect to the FC-7 input (we exclude external MIDI messages)