Folders having multiple reincarnations on clients

Hi,

We are running a Mac OS X Leopard Server 10.5.8 on a Intel XServe. Most of the data is stored on the internal disks. When clients (mostly Snow Leopard) connect to the server and use it normally for a while (storing files, saving to the server's share points) it happens sometimes that some folders are showing up 2-10 times, all with the exact same name and content or some folders are missing or have no content at all. This phenomenon is visible for some seconds and on more then one client on different folders. Sometimes folders a showing up and get hidden all 1-2 seconds.
I tried the following: I cleared the caches in the library folders, I installed a combo update, deleted all .DS_Store files on the share points and checked the hard drives, nothing helped. Interestingly this does not happen on a share that is stored on a external RAID System which is connected over FW800.

Is this a known issue? What can I do about it?

Thanks for reading
Philip