I was going to afk at my gold farm in the newest snapshot (15w38a) when I noticed that items and experience orbs weren't getting launched when a piston pushed a slime block into them. I further tested this and it seems like even players do not get launched off slime blocks.

*What I expected to happen was... *
To be launched off by a piston with a slime block.

What actually happened was...
I slid right through the slime block and items just got pushed up one block.

*Steps to reproduce.. *
1. Place a sticky piston with a slime block attached to the extending arm.
2. Place yourself or items on the slime block.
3. Power the piston.
4. Notice how you or the items are not launched by the slime block.