Comment 49 for bug 630383

OK, more info! I now believe this is actually a gnome-terminal bug that appmenu-gtk merely exacerbates. You can reproduce on stock gnome-terminal by:
1) Logging into a fresh session
2) Open a gnome-terminal
3) Click on the Edit menu
4) Now try to copy some text and paste it. It will copy, but not paste

This is because when the Edit menu is activated, if no content is in the clipboard, gnome-terminal will disable pasting. But it doesn't notice when you do put content into the clipboard. Normally this isn't a problem since pasting starts enabled and you normally don't open the Edit menu before there is content in the clipboard. But appmenu-gtk forces a fake activation of the Edit menu (for its own, valid reasons) that causes pasting to be disabled on startup.

So I'm working on an upstream and a distro patch.