120 FPS But Multiplayer-esque Lag in Singleplayer

While playing singleplayer on 1.8 I've noticed an issue where my client gets out of sync with the local server, blocks do not drop anything, can not access inventories, redstone doesn't update, can't pickup item drops, can't attack mobs etc. The console keeps printing the "Can't Keep Up!..." message and when the server skips 100+ ticks to re-sync my character is teleported back to where I was when the server de-synced and all the blocks I'd broken would come back. During this whole thing my framerate doesn't drop below 120. My rig is more than powerful enough for me to play singleplayer, especially with the new optimization that 1.8 brought. So it doesn't seem to be a hardware issue, but a software one. EDIT: The crash report isn't mine, my client has yet to crash. This was uploaded by a user who is watching the topic.