Ohh, sorry, it's true it's late in Sydney , here in italy we are still on the 21 Anyway, I erroneously thought that it would have been the same to use the original model instead than the one with only the copy-pasted part. You rightly showed me I was wrong. Soo, uhm uhm, I'll try to work on a copy-paste part on another file and reimport it on the original mode.. But that's a really crappy bug, since I am always careful to my geometry and I clean and verify my model often. Thank you Box!