Regardless if I'm on Singleplayer or Multiplayer, I get one of two issues.
1) I'll just be walking around or building when all of a sudden my character walks forward without me even having my fingers on the keys. The only way to get out of this is to either go into the inventory or the pause screen.
2)At random times, with no way that I know of to trigger it, I can't freely move items around in my inventory. It stays stuck on instant shift clicking.
Fyi this has happened to me since 1.4 came out, including the pre-release.