If I was to hazard a guess, I'd say that whoever installed the earpads (not me!) on your R10's must have put them on slightly improperly. If you look at your R10's, you'll notice the left earpad is fixed on at a slightly different angle/rotation than the right. In any case, what I would recomend doing is finding what type of glue needs to be used, and reapply both earpads yourself. I was going to do that, but decided the new owner might like how it is.
IIRC, there was a posted thread, with pics, on replacing the R10 pads. The most difficult part of the job was removing the old adhesive completely. Sounds like your pads were re-applyed over some glue residue, and sit unevenly because of that.