Falling onto a slime block such that the centre of the player is not over it will not trigger the slime block to bounce/negate fall damage (etc.), even if there is no other blocks contacted. I believe that this would be expected behavior if another block is present, but not with air - the only block being contacted is slime.

Reproducing:
Place a slime block above all adjacent blocks. While standing on top of it, hold shift until the centre of the player is no longer directly above the slime block, but you are still standing on the slime block. Use commands (or creative flying) to teleport up 10 blocks or so. There should be no bouncing effect, as if landing on a non-slime block.