When ice is placed under soul sand, it will make the soul sand's slowness more effective.
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[media]

This is the most noticable bug. Even a noob can try this and see that it is true. Soul sand above ice can make you move a block every 2 seconds.

Why was this marked as duplicate?
It should be marked as related to the other report, as that one is SLIDING, not SLOWING DOWN.
Big difference!