In just one of my worlds, the game ticks seem to slow down. Levers take over 15 seconds to change states when pulled. Doors take the same time to open when activated by redstone.
This only happens in certain areas. For example, inside a floating structure I am creating, where the outside world is not visible at all except through glass, the framerate and ticks are fine. But whenever I can see the outside world NOT through a transparent block, the framerate slows to about 20% of its standard rate, and the game ticks slow.
Sometimes, it jumps to about 70% normal framerate, and the tick rate becomes normal for just a split-second, but then everything goes back downhill.
This was NOT fixed yet. At least the phantom fire charges in my last post have been.

Note: I am using some Minecraft mechanics exploits. One device that exploits it is a wireless redstone transmitter. However, this is not causing my problems. Even when I turn the transmitter off, the problem persists. However, I am wondering if it has something to do with the fact that it's just there.

Another note: Only ONE of my seven existing Minecraft worlds actually has this problem. This does not occur when playing on a multiplayer server or LAN world.

EDIT: I accidentally labeled it as "crash". That was wrong; there is no crash. It's just a bug. I removed the erroneous label.

EDIT: Another related problem was found. When I open the bugged world, the game takes me back to the home screen. If I wait for about 30 seconds, it successfully loads, but it takes another 30 for the 1st chunk to start loading, which means that I start falling, falling, falling until the chunk loads and I am correctly positioned.