On Tue, 10 May 2011 11:26:43 +0200, Marco Weber said:

> As you see the directory has 500 permissions. ( On all other machines 
> the /proc has 555 permissions. )

> This is the kernel that is running:
> root@m88:~# uname -a
> Linux m88 2.6.38.2-grsec-xxxx-grs-ipv6-64 #1 SMP Fri Apr 15 17:44:15 UTC 

Aha.  "grsec".

You run a kernel with grsecurity compiled in, this sort of stuff happens by design.