If you explore the edges of a slime block you'll notice that two sides are bouncy regardless of how close to the edge you are and the other two sides are rock solid if you land on them.  A fairly large chunk of the slime blocks do not bounce the way they are supposed to.  It seems like the area designated to be bouncy somehow got shifted over to a location that doesn't quite make sense.

IIRC the very edges on all sides of a slime block are supposed to be solid (Unless attached to another slime block) and the center area is supposed to bounce you.  This being off is really off putting to parkour players and others who rely on slimeblocks.