As per this thread there appears to be a Simulator bug where a 1px line is clipped off the edge of images when using affine transforms. I initially thought I must have been doing something wrong as graphics programming is a new topic for me, but another forum member confirmed that they are seeing the same thing.
The top sprite is simply rotated and does not clip; the bottom three use affine transforms to do horizon and vertical flipping as well as a 90 degree rotation. Interestingly if I do a transform that doesn't align perfectly with the grid (e.g. a 45 degree rotation) this doesn't happen.
This is happening under both 1.9.0 and 1.9.1 on macOS; unfortunately I don't have any other machines available to test on.
The issue's in the tracker and I'll give it another stab as soon as I can!