Running nautilus hijacks my window manager

[Chris G]

When I run nautilus it does something diabolical to my window manager!

I run fvwm2 as my window manager and it's lovely.  However if I start
nautilus it clobbers everything, the background colour changes
slightly, but more to the point I can no longer get my mouse menus by
clicking on the background.  What's it doing and how can I get my
fvwm2 back apart from by shutting down and restarting (which in itself
is quite difficult because I normally do that via one of the
mouse-click menus)?