I don't believe it's a bug. It seems to me the issue is that your using tiled backgrounds which don't give the ability to draw a collision polygon. I'm sure this is due to the fact that they can be resized and tile automatically. If you use sprites, you won't have the issue. Tiled backgrounds seem to create an imperfect collision polygon oversized to the actual size of the background.
I changed it on overlap added System wait 1.0 before changing the Move value to 0 worked better.
Using "on overlap" works better but, if you need to use tied backgrounds I suggest the following:
Use a larger sprite for the Blue block to 64, 64. Then draw the collision polygon undersize within the image editor for the Blue block. Then just resize the block down to 16,16 in the properties dialog box. Use "on overlap" instead of "on collision" and give it a delay before changing the value of Move to 0 as said above with the system wait.
I'm sure Ashley could elaborate better as to why the Tiled Backgrounds work differently as solids than sprites since you have no ability to draw collision polygons.
I'm using windows 8.1