After some further invesigation I found that the problem also occurs
with the 'Elegant Brit' and 'Elfin2' themes. However this may be of some
help, as I recall using Elegant Brit previously (on hardy I think)
without these problems, so it seems to have something to do with either
an upgrade of gimp
I'm having a bit of a problem with some Gtk themes that I've tried.
Several Gtk themes seem to really mess up the rulers in GIMP, such that
they are pretty much just a solid black area on screen, and I'm not
really sure why. There are lots of themes that seem to cause it to
happen, the most recent