This seems to be common, as mine is the same way. It seems to be related to the construction/design of the keybed, since I find it's consistent especially between each A and B key across the bed. It's almost as if the keybed is modular, with each octave of keys (from B to A) being a single section, and they're all connected together, and the junctions aren't perfectly aligned.

Looking edge on to view vertical alignment, each A key is slightly higher than the B next to it, and this repeats all across the keybed. And on mine, the spacing (when looking down from above) seems to be off some too, with each B key being a little closer to the C next to it.

The good news is it is just an aesthetic issue, on mine at least, as it doesn't affect the feel or playability. I had a Motif XS6 in the past and its keybed was nicer, but of course it was also a more expensive model, like the Montage now. I figure it's a small price to pay for a much more affordable yet powerful synth. If not for the MODX, I would have to do without as I can't afford the Montage.

Thank you Kevin for your insightful answer. I am buying a MODX7 this November and as I said I have tried one at a local shop. Liked it very much since I love light action keys that let you play "into" the black keys, and most of the semi-weighted synths / Midi controllers you find nowadays make it very difficult to play the black keys near where the hinge is (near the beggining of the key). This may seem a bit paranoid but it is not for sure. Some chords require your fingers to be placed well over the mid lenght of the keys (and even further) and this is where a well balanced hinge mechanism detaches itself from the others.

They had a Nord Grand (Kawai key mechanism) at the shop and when I tried this keybed it was (to me) miles and miles away from the other top keyboards, including a Korg Kronos 88 and even the Montage 8. The lightness of Kawai's mechanism is astonishing...

On semi-weighted keybeds like the ones on Motif XS6/7 / Montage 6/7 (Yamaha FSX) you can play the white and black keys the way I described. So all in all you are absolutely right. Even with this small misalignments, the MODX is a great instrument. I played it with headphones and the quality, definition and fidelity of Yamaha's sounds (synthesized and acoustic) is really superlative.

Although the most important in the end, besides all this wonderful technical considerations 🙂 is if you make good and beautiful music to share with other and also delight yourself while playing and hearing it.