When pushing a slime block into a player who is flying, they will stop flying and fall; this does not happen with other blocks such as stone or honey. After looking at update history for slime blocks there does not appear to be a reason for this change.
Steps to Reproduce:
Recreate this setup:
[media]
Stand on the slime block
Fly upwards
Place a pressure plate below yourself
Observed behavior
After the slime is pushed up, you fall down (your flying is cancelled).
Expected behavior
The player would remain flying after the slime is pushed into them, consistent with all other blocks.
Please provide some screenshots and/or videos of this issue occurring whilst the F3 debug screen is enabled.