certainly a curious problem, as i have been building with gtkhtml3 without having any menu problems.

but i have to say that gtkhtml3 is at the (rational) end of its productive life with xiphos. our main, normal display toolkit today is webkit, and all our normal builds use that. i suggest that you uninstall the version you've got, then go to this page to learn how to get our ubuntu builds:

http://xiphos.org/download/debian-ubuntu/