Hi, I discovered a strange behavior with some imported OBJ-Files. See attachement. On the left after importing - everything is fine. I can fully work in the imported object. On the right how it looks after clicking the symmetry. It's an exported OBJ from 3D-Coat. You can download the OBJ here to discover what happens there: www.active-rendering.de/media/test2.zip
I have tried other OBJ (triangulated before exported to OBJ with C4D) and there it didn't happen. Cheers Sascha
That looks like expected behavior with the current method of implementing symmetry. Symmetry currently requires both halves of the object to be identical, in fact there's only one half stored and drawn twice, flipped and not flipped. So when you enable symmetry, it will throw away half the object and mirror the remaining half to make a symmetric model. It looks from your screenshot like the ball wasn't perfectly aligned with the middle line, so it turned into a butt.
Some of this might change in the future, but for now it's just how it works.