I go to the nether an after a little bit the game crashes. crash does not happen if i go back to the over world.
What I expected to happen was...:
the game to not crash
What actually happened was...:
The game crashed
Steps to Reproduce:
1. Go to the Nether
2. Wait a bit.
Time for crash varies
On one game, it starts in the Nether and immediately crashes.
In another downloaded map the game seems to crash in one place in particular.
Problem did not start till that map was downloaded.
Map is Gloria 2.
Fixed problem by force updating
Linked issues
Comments

You could have just added the additional info as a comment for MC-2321.
This same exact thing happens to me, but only when I am playing in 1.4.2 server version. Singleplayer is fine. I am not using gloria. Also, server uses bukkit, but I don't think that is the problem.
This is not a valid report. No crash report.

Please update your java to the latest version, that has helped now in several similar cases. See MC-2749 and the duplicated issues.
Firstly, you should post a crash report. Secondly, if you fixed the problem by forcing an update, then what is the bug?