If VO is started in windowed mode, a proper window title is set. If started in fullscreen, then changed to windowed, no title is set. I noticed when trying to match the window's title with devilspie. For example, to pin VO to all of my workspaces.

It might be useful to let the devs know what distro and desktop environment/windowmanager you're using when you have this problem.

This happens no matter what window manager I use, or whether or not a compositing manager is used. Arch 64 bit, BTW.

It also does that if I change the resolution.

I've had a very similar issue since some update last summer.
Linux Mint 10, 11, 12, Gnome Desktop:
No window title, not even recognised by the window list. That's independent of full-screen or windowed modes. Compositing makes no difference either, nor does the window manager (compiz, gnome-shell or metacity).

For gnome and compiz try installing compizconfig settings manager

Then from Utilities / Workarounds and select Legacy Full Screen Support

This will give you full screen all the time and yet you can ctrl+alt+left/right arrow to move from desktop to desktop and still utilize the convenience of windowed mode but yet have full screen
or depending how you have your desktops setups in a row or in a grid you can ctrl+alt+up/down arrow etc.

Anyhow hope this helps