Slowness happens 1 block ABOVE Ice

You walk slowly when walking on the edge of a block which is next to ice/packed ice which is one block lower. I'm pretty sure this is only supposed to happen with slabs and Soul Sand, not full blocks.
To recreate just take a flat surface, dig a two-block-deep line and fill the lower layer with Ice or Packed Ice, then walk on the edge while almost floating above the Ice.
See screenshot.

Device: Samsung Galaxy SIII Neo (GT-I9301I)