Affects Version/s: Snapshot 13w10b, Minecraft 1.5, Minecraft 1.5.1, Minecraft 1.5.2, Snapshot 13w18c, Snapshot 13w19a, Minecraft 1.8.1-pre3, Minecraft 1.8.7
Fix Version/s: None
Environment:Mac OS X 10.6.6
java version 1.6.0_22-b04-307
I found a weird bug a while ago. Sometimes, when you power a double extender with pistons facing up with redstone going in to it, either the top or the bottom one will fire.
How to replicate:
1. make a 1 tick pulse shortener by placing redstone, a piston with a block on top next to it and a repeater behind that (as in the pic).
2. connect a redstone wire to the repeater and go one block out every other block and put redstone on top of that (like in the pic).
3. place 2 pistons on top of each other at the end of each redstone wire pointing out, so the wire goes into the pistons.
4. press the button.
Note: you won't always get a weird result, it's very un-predicatable.