Is this where I'm supposed to report bugs? If not, I apologize.
1st, this one has happened since after 4.5 BETA 14: The texture editor is messed up in the paint room. There are jagged edges around the UVs that make it impossible to see where the texture actually is. You can see details with screenshots in this thread: http://3d-coat.com/forum/index.php?showtopic=18305
2nd, the Quad tool in the retopo room causes me massive lag in version (Win) 4.5.16 with a high poly mesh. When I reverted back to BETA 14 (because of the above issue), there's no lag.