I have Illustrator CC 2014 running in Mac OS X 10.9.3, and discovered tonight while making a test pattern that if I do an offset path of -0.0005" it doesn't calculate the size of the resulting objects correctly. If I do +0.0005" it works fine, if I do -0.0015" it works fine. I obviously haven't tested exhaustively, but there is definitely a reproducible error there. It's not even off consistently in the width and height. The sizes listed refer to the size of the individual squares in the 4x4 grid of filled rectangles.
