[iBook] disappearing finder windows

[ibooklist2 at matthurst.fastmail.fm]

Intermittently, Finder on my iBook (running 3.9, with Screen Spanning
Doctor for my external screen) stops showing windows. It's running, and
the list of windows which pops up from the icon in the dock shows the
what it should, but no windows appear. The computer runs fine apart from
that, and it's sorted out by a reboot. Anyone had anything similar/ any
ideas?

cheers

Matt