You can walk into glass!

Can confirm.

Not glitch. in source it is marked as a Special Block. some of these are Slabs, Leaves, Glass, Iron Bars, Glass panes, Vines, Grass, Lava still, Water still, Mushrooms, Reeds. as you notice all of these blocks have a point were it is see through. try with all these blocks and you will see (water and lava must be still, u will need a Inv edit (toomanyitems have it, not NotenoughItems tho using an inv edit will make this test invalid, but it gives you an idea of whats going on)).

Duplicate of MC-2164.