When I start up my MOXF the Transpose Button is already engaged and has shifted +1.

Can't speak to the MOXF but for the Modx the only way transpose gets changed globally is if the user changes it.

Here's what you can do:

1. Test to see if the MOXF saves the transpose setting after a power down. Turn ON the instrument - do a transpose - then turn off the instrument. Is the transpose setting the same as you set it when you power on?

2. Reset the setting by pressing both buttons at the same time - per the Owner doc page 12

MOXF6/MOXF8 Owner’s Manual
Control and Functions
13
% TRANSPOSE [-] and [+] buttons (page 27)
Use these buttons to raise or lower the pitch of the note in
semitone steps. To restore the normal octave setting, press
both buttons simultaneously.

I've turned the synth on and off with the Transpose OFF entirely. When I turn the synth back on the Transpose LED is lit and it's one semi tone (not +, I mistated that) DOWN. But it is NOT retaining anything from the last Song loaded. It just "defaults" to Transpose - 1.

I'm thinking perhaps I should reload the OS and see if it corrects itself. If so, what IS the latest OS for MOXF and what is the proper and safest way to reinstall it?

I'm guessing the transpose + button is incorrectly stuck "on". The same thing would likely happen if you power on a perfectly functioning MOXF and hold the button down as you turn it on and wait until the board comes up fully with the button pressed.

There is a button test in service mode that can flush this out at least to diagnose.

Probably would get it serviced.