Hmmm, I've had this happen, only with cheddars, and frankly, it didn't bother me. I just thought it was a sign of very aged cheese. OK, I liked it. Guess I'm weird!
If you really want to know if it's acceptable, I'd suggest you call Neals Yard Dairy or La Fromagerie in London - 2 of the best cheese shops around. If you got the cheese at a deli or specialty shop, it might be acceptable for hand crafted cheeses. For commercial cheeses such as in the dairy aisle at Tesco, it might not be.
I'm not sure what Melissa posted is what your are thinking of. I could be wrong, but I think there's a difference between surface white stuff and crystals within the cheese.