I tried to recreate a memory leak I found in 1.6.2 and instead got a different bug.
When I explore a single-player world too fast, the chunkloader loads too much data in too little time, and a possible memory leak causes an inevitable crash.
Doesn't affect multiplayer servers.
Steps to reproduce
Load or create a 'normal' single-player world with creative.
Use Zombe's modpack (which isn't out for 1.7.2 yet) to fly at 10 times normal speed and explore the world for a couple of minutes.
Alternatively: Type /tp 0 100 1000 and wait for the ground to show up, then increase the z coordinate with 1000 and repeat.
I'm using default memory allocation in case of Zombe's modpack and 256MB in case of /TP-ing.
Can keep exploring the world indefinitely.
After about 2 minutes of flying (or about 6 times /tp), video starts lagging. When continuing to explore, the lag becomes as severe as hanging ~15 seconds, and will cause an OutOfMemory exception, a died thread (the Server thread). and weird behavior
This weird behavior is: the ground doesn't show up and cheats stop working. When going back to the menu and trying to load the level again, it freezes hard (I have to terminate the process).
The 'Used memory' in the F3 screen never reaches 100% even when the crash already occurred.
The two logs are from two different instances of me successfully recreating this bug.
FYI, what happened in 1.6.2: I get a neat menu-like error message with the options to exit or go back to menu. When selecting back to menu, I see the server list instead of the main menu (even though it was a single player game).