kaleb bacon

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)).

And it isn't discolored just darkened

as this is a glitch it isnt just the block turning dark, try animals you will see

Thats not a bug. if you have an enchanted item in your hand it will sparkle while paused. pausing isn't suppose to pause animations just movment.

This happens because minecraft unloads chunks meaning all animals, mobs in them are despawned.