Unfortunately, there's nothing much useful that I can actually tell: running the vendetta executable in a terminal simply prints, "Segmentation fault" and running it in gdb just prints:
"[Thread debugging using libthread_db enabled]

Program received signal SIGSEGV, Segmentation fault.
0x00325a15 in ?? ()
from /usr/lib/libgtk-x11-2.0.so.0"

using the theme found here: http://hugo-kde.blogspot.com/2010/11/oxygen-gtk.html. Workaround: switch the GTK+ theme used (in KDE, System Settings --> Appearance --> GTK+ Appearance; in Ubuntu Gnome, System --> Preferences --> Appearance; in other Gnome set-ups, run 'gnome-control-center' and click Appearance).

Ugh. Same issue. Changing themes to default Raleigh fixed. Thx!

Odd. FYI, I'm pretty sure it's possible to set up environmental variables so that programs launched from that environment will use an alternate theme, so you could make a wrapper script for running vendetta that would cause vendetta to use Raleigh or whatever without having to change your overall theme.

FWIW though, it sounds to me like the bug is with either GTK or (more likely) the theme engine, rather than with Vendetta, though it is possible that Vendetta's updater is trying to do something it shouldn't that somehow only causes problems with certain themes.