It looks like I was able to narrow down this bug quite a bit. Its a bit of an edge case im sure, but it greatly effects my work flow since I use a lot of tubes/splines and mirror them. The original thread is here.
https://forum.corona-renderer.com/index.php?topic=17444.0Max 64B 2017 and Corona 1.6SP3 and 1.7 Nightly.
I can reproduce this bug 100% of the time and have found a work-around for the short term.
#1, create a long tube with 32 sides and no height segments and unwrap it normally.
#2, create a copy (I shift drag) of the tube and mirror it.
#3, create a slanted box intersecting 1 or both ends of the tube to cast a shadow/AO
#4, bake an AO or Beauty map. The mirrored cylinder will render poorly showing the incorrect UV mapping. If you apply the texture after bake, the mirrored cylinder's texture will look incorrect.
It seems to be a function of both the MIRROR and long tri's/quads. IF I subdevide the object, it will FIX the poor texture baking. Right now my work-around is to subdevide the mesh before baking. This seems to be working. Also the bad baking does not effect scanline, Mentalray, or Vray using the same objects/UV's.
Kevin
