Mirroring right/left : causing topology change?

Hi there,

Trying to regain symmetry on my model, but when i do a right to left mirror, it looks like the geometry is getting cut and welded in a different way.

That is probably not whats happening, but i’m not sure — any ideas?

Is It possible those polygons are non-coplanar and Nomad divides them so???

I’ve experienced this often. It only seems to happen when there are edges along the mirror plane. I got round the problem by having symmetry set to world and then always moving the object a tiny fraction so that the edges no longer coincide with the mirror plane before doing the mirror action