Icons for closing/maximizing/minimizing windows are gone/invisible using HighContrast theme

After upgrading my LTSP environment to precise, users report that they cannot close/resize windows anymore because the appropriate icons are missing.

Investigation reveals that the icons are not missing, but simply invisible, which has the same effect for users who are not IT pros.

This happened after upgrading to 12.04. A fix was released for 13.04, but given that 12.04 is LTS, the problem needs to be fixed in 12.04 as well.

Environment: LTSP set up as described in the Ubuntu wiki, thin clients booting via PXE. This means Unity2D is used.

#964685 seems to solve the problem for 13.04 (untested), this bug is for Precise (12.04).

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-accessibility-themes 3.4.1-0ubuntu1.2
ProcVersionSignature: Ubuntu 3.2.0-38.61-virtual 3.2.37
Uname: Linux 3.2.0-38-virtual x86_64
ApportVersion: 2.0.1-0ubuntu17.1
Architecture: amd64
Date: Sat Mar 9 12:08:18 2013
Dependencies:

InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110426)
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=de_AT:de
 TERM=xterm
 PATH=(custom, no user)
 LANG=de_AT.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-themes-standard
UpgradeStatus: Upgraded to precise on 2012-05-17 (295 days ago)