There was one major change in this release:

• Changed the algorithm used to make many of the cave surface features.

This has many side effects:

• Different looking cave surfaces (duh)
• Mycelium is more dense in the mushroom caves
• Cave surfaces are now multiple blocks deep (this includes some of the ice patches in frozen caves)

One more unrelated change:

• Smooth Basalt and Basalt surfaces now appear in molten caves above y=0