I just realized that I had completely forgotten about selections. When you transform a selection no only do you transform its contents (I was already doing that), but you also have to do the same transformation to the selection shape. However, I'm storing the selection shape as a region, and the region format is an opaque data type, which I cannot access directly. Apple has provided no flip/rotate commands for regions. But I discovered I could draw the region into a temporary GWorld, do the transformation on that GWorld, and then use BitMapToRegion to convert it back to a region. This should of worked in theory, but when I tried to implement it it failed miserably (causing hard crashes too). I guess I'll have to leave this matter to next year :p