I know this is an old thread, but this was the closest hit to my problem when I searched.
My keyboard was giving me "om" when I pressed "o" or "m". It did the same thing on many PCs. I couldn't find any solutions online, so I figured I should open it up and check it out. I cleaned the inside a little, and gave the plastic membranes (in my rubber dome switch K400) a little wipe down. It didn't seem to work at first, but I tried again in a while and the problem went away. So I'm not sure what fixed it, but I guess it wouldn't hurt to open it up and clean and jiggle the parts around a bit. Just be careful not to snap any little ribbon cables while you're at it.