Operating system: Windows 7
Graphics card: GeForce 660 x2
Cryptomatte seems to be eroded or feathered inward, leaving a halo around the edge.
Exact steps for others to reproduce the error: Duplicate default cube multiple times, enable cryptomatte by object, enable 'Accurate Mode', render in Cycles with CPU. In the compositor, isolate a cube with the cryptomatte, use a color>multiply node to give it a color, and put it on top of the original image with an Alpha Over node. Observe halo.