Traveling to any dimension tends to make blocks break super slow as if you don't have the hardness requirement boost anymore. Exit to menu and restart usually fixes it.

I had this happen to water walking too. Before reloading, trying to walk on water created the same effect that used to happen often when you would jump on farmland to flatten it and get stuck bouncing.

This also prevents the use of the teleport power.

Agreed, this and a few other bugs need to be fixed, as they cause issues that completely break the game. I've lost so much progress doing this. I really need to progress, and having to revert to a backup every time I glitch out, is a real problem.

I can confirm this on the Direwolf20 2.2 pack with monk mod added.
going to the nether and break a block bare handed causes the block to desync. it removes it on screen but remains as invisible in game. Flight does not work there, and armor icons do not show up.