I like to use the GNOME desktop, but I prefer to replace its window manager with openbox, with 4 workspaces. However, when I run openbox --replace, the number of workspaces available drops to 1. If I go into obconf, workspaces is still configured to be 4 (~/.config/openbox/rc.xml shows the same). I can get the workspaces to reappear by changing the value in obconf to anything else, and then back to 4.

I have just been dealing with this problem since Ubuntu 9.04 (now up to 10.10) since I don't reboot very often. But it's really annoying to have to reset my workspaces whenever I do have to reboot. Changing the value in rc.xml and running openbox --reconfigure does not seem to have any effect. So what is obconf doing that I'm not (sends a dbus message perhaps [EDIT: watching with dbus-monitor I see no messages when changing the workspaces value in obconf])?

I was hoping there would be a cleaner way to change the window manager than just running openbox --replace at login. So my questions are:

1. Is there a better way to specify an alternate window manager (i.e. a way that doesn't cause the workspaces to break)?
2. If not, how can I automatically set the number of workspaces back to 4?

Update:

I finally got around to trying what I commented on MrShunz's answer (adding WINDOW_MANAGER=/usr/bin/openbox to ~/.gnomerc). But the effect is the same as openbox --replace.