Slime block player launchers are finicky

I was trying to make some slime block launchers for my base and found that slime blocks are kinda.....finicky. Some of the time it would launch me in the air, other times it would glitch me through the block and i would not get launched. I played around with versions and found they work perfectly fin in 1.8.8, but all 1.9 snapshots seem to be effected.

https://www.youtube.com/watch?v=d7Uw2ObvUX4
At 4:30 i start messing around with the pistons and you can see how they act.