This is not a bug, torches have never been able to take 1 tick pulses, and this behavior has been used in countless redstone contraptions. If you want to power a torch, just put a 2 tick repeater in front of the observer.
Not a bug, comparators has never been able to take 1 redstone tick pulses.
Confirmed.
Still confirmed for Minecraft 1.9 Pre-Release 1
This isn't a bug, falling blocks are really just entities, and they don't have any collision with each other, therefore they are able to pass through one another.