Ok - you can
get updates without synaptic.
This look very much like bug:
... mentioned before. Did you read that report?
One user reports that resetting gnome to defaults did the trick: that involved removing
.gnome .gnome2 .gconf .gconfd .metacity
... from the home directory.
I don't see anything explicitly synaptic-related in there.
I also looked for apt, aptitude, apt-get, and update manager. Nothing promising.
Personally, I'd try removing and reinstalling synaptic using aptitude.
I think you need to answer to the bug report with your error message about gtk buttons, and what happens with synaptic reinstall.