Powering Adjacent Dispensers or Droppers from above fails

2 (or more) adjacent dispensers or droppers powered from above work correctly once, and subsequently only 1 fires.

What I expected to happen was...:
Both dispensers would fire whenever powered.

What actually happened was...:
Both dispensers fire the first time, but then afterwards only 1 dispenser fires. Breaking and replacing repeaters resets the behavior.

Steps to Reproduce:
Place 2 dispensers next to each other, with solid blocks above them. Run repeaters into the blocks above, and power those with redstone dust powered by a button.

This behavior is not what happened in 1.4.7 and is new to 1.5 This does NOT seem to be a duplicate of any piston issue. When replacing the dispensers with pistons, both pistons fire correctly.

When powered similarly from below, this problem does not occur, only when powered from above. I have also been able to duplicate this without the repeaters, running redstone dust on the blocks above the dispensers.