I was fooling around with the new block types in creative mode and I assumed that the slime blocks would work exactly like the soul sand blocks (soul sand blocks slow you regardless of where you stand on it), however I noticed that if you go to the very edge of the slime block, you do not get slowed and you walk/sprint at normal speed.

I tested this in creative and survival, and the bug exists in both.

To reproduce this bug, simply walk on the edges of slime blocks.

I am unsure if this is intended or not.