Home dirs work, but only for a bit…

OS X server (PPC) 10.4.8 with XRAID people can log on no problem at all with home dirs but after about 20-30 minutes they seem to lose contact with thier home dir, any volume mounts are still good but if they launch mail thier preferences are gone and they are asked to set email again, or if they launch safari thier shortcuts are gone, basically it looks like they've lost ~/Library access.