Directory listing fails for specific user

[Philipp Marek]

> We have recently had a new problem with one of the users on one of our servers. 
> 
> Filezilla claims it connects and authenticates, but then fails to list 
> the directory (although no error message is output, it just eventually 
> times out. There is the full output of filezilla located here: 
> http://pastebin.com/tAVcSP8Y. 
...
> I do not get the same issue for other users on the same server. For 
> example, the output of a working user connecting to the same server is: 
> http://pastebin.com/6VtcCPhg (filezilla) and http://pastebin.com/9ETc8JSS 
> (openssh). I'm at a complete loss as to what may be causing this and 
> cannot find anyone on t'internet with the same issue. 
PMTU detection goes wrong, and the specific user has a directory with too 
many entries?

Try to list /usr/bin/ as various users, and/or reduce the MTU for testing.