It crashed three times, all when pushing a redstone block with a normal piston:

• first and second crashes: The pushed redstone block powered a command block, making everything sky-colored and crashing.
• third crash: Trying to crash the game this time, I pushed a redstone block with a normal piston without the redstone block powering anything, and it didn't crash. For some reason I was able to retract the piston, even though a piston with a redstone block at the end wasn't able to retract in 1.9. I extended and retracted the piston a couple of times quickly, making the screen sky-colored and crashing the game within seconds.

What I expected to happen was...:
the piston pushing the redstone block, powering the command block (first and second crashes)
the piston pushing the redstone block, unable to be retracted (third crash)

What actually happened was...:
it crashed immediately just after the screen turning sky-colored (first and second)
I tried to replicate the first two crashed without the command block (nothing being powered by the pushed redstone block), in 1.9 it would extend once powered, not not retract until the redstone block it pushed was removed. But, once I unpowered the piston it retracted, leaving the redstone block pushed away from the piston. Then I extended and retracted the piston a couple of times, crashing the game like the first two crashes. (third)

Steps to Reproduce:
1. push redstone block with a piston to power someing (I only tried a command block)
OR push redstone block with a normal piston repeatedly
2. watch screen turn sky-colored, like the blocks all disappeared
3. ???
4. profit (in crash money)

all crash reports are attached in chronological order

(get it? CRASH money?)