when blocks have a slipperiness under 0.6
players and mobs which is walking or sprinting will have a higher speed than normal.

slipperiness at 0.3 result in ~5 times normal speed
0.15 result in more than 30 times the normal speed
which is unusual

(just some thought on it)
maybe it is the simulation of the "sliding" which makes it happened
which means:
high slipperiness: low acceleration, low friction
(you gradually gain speed and reach a limit)
low slipperiness: high acceleration, high friction
(you instantly gain a lot of speed and outweigh the effect of friction)