Lost AFP Permissions

Hey all, Odd situation I'm having. I have several users, both using 10.4.8 and 10.3.9, that connect to an AFP share on a file server that is hooked into OD (both the file server and OD Master are 10.4.8). The clients are also on this directory, but they log in with local accounts. After some seemingly random amount of time connected to the share (hours->days), they lose permission to access data on the share. Getting info on any item in the share reveils that they have no access, but the group access still is still accurate and these users are members of that group. Access sometimes is reestablished after some amount of time, or unmounting and remounting the share fixes it as well. I have set noNetworkUsers=yes, removed and readded the users to their groups (which is another odd issue: if I add the group from the user pane of WGM, checking in groups shows a user unknown, but adding the user from the Group Pane works), I've disabled forced logout when idle, and checked all the logs I can think of to find the issue, to no avail. Everything "looks" fine, but it still happens. I enabled afp debugging on the clients (level 6), and nothing shows odd in the logs. The 10.4.8 client was running 10.4.3 and did the same thing. I can only imagine it's the file server getting confused and losing track of who the user is, and/or what group they are in. I've thought maybe making the file server an OD Slave might help since it would have a local copy of the directory... but that's assuming this is a server directory issue (seems logical since it impacts more than one client). Anyone have any suggestions?