Please see attachment.
To recreate the bug, build this device in any direction.

What I expected to happen:
The redstone signal to be received by the comparator and transmitted onwards, since the comparator is not on subtract mode.

What happened:
No redstone signal was received by the comparator.

Note the placement of the button, this glitch only occurs when the power coming into the comparator's side is greater than the power coming through its back. If the back signal is equal to or stronger than the side signal, it works fine. Note that this test works as expected on subtract mode.

Note that I tested it in both 1.7.10 and 14w28b. I got the exact same result both times.