Spaces keeps switching to finder space of it's own accord every 2 min or so

Not sure what is causing this intermittent bug. I'l be in Mail (Space 8) or Safari (Space 7) and the OS switches to Finder (space 9). It might happen as much as every minute or as little as every few minutes. Usually a reboot makes problem go away for a few days.

Wondering if it's something like dropbox activity or just a Leopard bug? Known issue?

Dual g5 PPC 10.5.8