Frost walker ice dosen't melt

Frost Walker ice dosen't melt.

(World was created in a 1.9 snapshot, last opened 1.9-pre4. Ice didn't melt, but in new 1.9-created world it works.
Not sure if this can still be specified as a bug.)

Steps to reproduce:
Get frost-walker boots.
Walk on water.
Watch as the ice fails to melt.