This is no longer relevant, since the PPA have updated to GIMP 2.8.10, which has fixed the bug. If you use Ubuntu 12.04 LTS, you only have access to the old GIMP 2.6 in the standard repositories. This is unfortunate since GIMP 2.8 have a lot of new useful features. The standard way to get GIMP 2.8 is to use the a PPA, as described here. This used to work fine.