VSync seems to be the problem. Turning it off fixes the problems I've described below. If you want to help confirm this issue, try turning off VSync if you've been getting this same issue. If you have not been getting this issue, try turning VSync ON and see if it messes up your game.

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Creating a super flat world to test snapshot features greeted me with unusual lag spikes where the screen would freeze and tear when trying to move. Lag spikes happen very frequently around 5 seconds in between on average with up to 30 seconds of the game screen freezing in place and the client becoming unresponsive.

My PC has blue screened at least once, but I was installing new graphics software while testing the game hoping it would resolve the issue and may have put to much strain on my build.(I have confirmed that it was the graphics card update that was crashing my system, not touching Catalyst ever again)

Game physics and events would then need to "catch up" after the delay. For example minecarts would travel in a straight line to rails they would then be on had the game progressed at regular speed jumping off and over other rails in the process.

Zombies groups when attacking a player in survival during a freeze would have the damage and knockback stack up and then be applied all at once afterwards. They once threw me up about 4 block into the air.

Riding a minecart helped reduce the chance of the game freezing, and oddly enough recording my gameplay with a recording software such as Fraps removes freezing occurrences entirely.

I suspect it to be related to a problem with my GPU but it doesn't explain why it only affects this version. I have yet to test the previous snapshots