Oh I guess I know what it is.
Is the WASD spacebar thicker than the stock one?
I'm asking because I had to chop the inside of some Cherry thick PBT in order to perfectly fit them to my Filco. Filco apparently doesn't like thick keycaps (the keycap completely sticks at the bottom out point because of the friction between the stabilizer and the keycap). It even leaves a mark inside the keycap!
Check if your spacebar has similar marks as shown in the pictures (it's pretty hard to see, you have to view it at a certain angle against the light).
Also, CM Storm and Filco designs are very similar, so this might be relevant indeed.
Stabilizer marks (sticky) Numpad 0ShiftChopped (no more sticky) Numpad 0Shift