I have that problem as well, but only with NURBS objects (usually minor things like eyeballs, &c). I just ignore it, but now I'm curious as to what causes this as well! What version of Maya are you using? For the record, I'm using 6.5. I heard that version is a bit buggy, but for the most part it's fine. I did not have that problem with versions 4, 4.5, and 5...