In creative mode if your boat falls into lava at high speeds then the player is unable to place anything or even break blocks instantly. I have been able to reproduce this bug in the overworld and nether. This does not happen if the boat just falls into the lava at slow speeds. When I found this out, I was on blue ice going really fast, then fell off into lava, where I then was unable to place blocks, place a boat, or even break blocks instantly. Sometimes I am able to break the blocks but not always, and this is all in creative mode. My player hand also disappears from the first person view.