evolution can't be maximized in gnome-shell

When moving the evolution window to the top border of the screen or pressing the maximize button evolution doesn't change to maximized status.

Expected behaviour: Evolution window get's maximized

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: evolution 3.1.5-0ubuntu2
ProcVersionSignature: Ubuntu 3.0.0-9.15-generic 3.0.3
Uname: Linux 3.0.0-9-generic i686
Architecture: i386
Date: Sat Sep 3 18:46:17 2011
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
ProcEnviron:
 PATH=(custom, user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: evolution
UpgradeStatus: Upgraded to oneiric on 2011-09-03 (0 days ago)