When I load a world made before the 1.6 update (eg. CTM map like Vinyl Fantasy) (Tried multiple ones) for finite amount of Time the world periodically freezes and compensates lags by speeding up time for short periods.
This occurs on versions 1.7.4 and later.

It seems the game has problems with loading old chunks. Every chunk loaded lags for some time and than stops. After staying a few hours in one area the game is finally playable but once you go and load new chunks the terror starts again.The game lags on no matter what difficulty, no matter what gamemode. It doesn't use up unusuall amounts of memory or computer performance. There is no FPS drop.

Some chunks are never loaded and later cause the game to crash.

You can place blocks instantly but can't break them. Any blocks you break reappear. You can damage mobs and they can damage you but they almost don't move. When the time speedup thing happens (usually when problematic chunks are unloaded) everything in the game speeds up 10-50 times. Furnaces smelt instantly mobs run and hit incredibly fast instantly killing you (skeletons are like machine gun firing tens of arrows a second launching you meters in the air.

I was looking at the minecraftforum and here for some solution but didn't find one.

I also tried creating new survival world in 1.5.2 and than loading it in 1.7.5 but it didn't happen, but when I load my CTM map made around 1.5/1.6 its unplayable.

I can include video of the behavior later if it can help.

Thank you for any help...