Short version:
I'm able to get a dropper/dispenser to get stuck in a powered state?, at the very least it is no longer reacting to being powered. Even pressing a button on it will not cause it to react in this state. But it will reset it to a working state.

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Long version:
So, was building a vertical elevator as per this video (the small one)
http://www.youtube.com/watch?v=eHRVOLeZsKU

But only the first item gets to the top, the rest got stuck in the second from the bottom.

Replaces the Droppers with lamps to trouble-shoot. Seems to work.

Replaces them again, but this time with Bonemeal-filled dispensers pointing to the side.

In the attached image, the one with a button on it only fires once if i trigger it all down to the right. Also, the first time i press the button on the Dispenser, it wont fire. (but the one above, and the one below does)

Second time i use the button on the dispenser, all three fire. And it will fire one more time if i press the button down on the right.

My guess is something in this causes the Dispenser to get stuck on Powered, which is reset when the button on the Dispenser stops powering it after being pressed the first time.

Why this only happens with one of them, and why the button on it can do what the other redstone doesnt seem capable of is the 2 main things that worries me a bit.

EDIT: It seems any block-update close to the failing Dispenser will reset it, but why the one a the top doesnt have the same issue beats me.
EDIT 2: If you extend it upwards, only the top one keeps working, so it seems the block behind and above being powered by the repeater and diagonally powering the Dispenser is the culprit. So probably your average bud-behavior which is now revealed when the other bug to them were fixed. (Se second image)