Why are unhidden /private/tmp directories created on shared network with Mac OS X 10.6.8?

I have posted this elsewhere (But not at Apple) with little response.

I have a group of 5 MacMini computers in our graphics department; they are all joined to a Windows 2003 Active Directory and use a shared drive space for file sharing/storage/backup. They all run 10.6 or a bit older OS, but this situation is created by a single workstation.

One of these users has a workstation running OS X 10.6.8 and a variety of publishing and graphics tools. At an unpredictable point, this workstation creates a /private/tmp directory in the root of the shared drive. The folder is unhidden (viewable by all users with access to the drive). There are no files left in the drive (some may be there at some point, but none have been seen by anyone during occasional investigations). If someone deletes the directories, a week or two goes by and they are re-created.

I know which workstation is authoring the directories due to the Windows permissions and owner of the folders.

I thought I would be able to locate the offending process and make it stop. At first, I thought the user's system might be creating it because there was little local drive space left (less than 1 GB Free) and using that area for temporary drive caching during a big Photoshop operation of something. I had the user empty the trash (about 20 GB); I deleted the /private/tmp directories, hoping I had fixed it. Three weeks go by and suddenly it reappears. I rush to the workstation, open Console, and examine all entries for the period when the creation occured. There was nothing going on at all. So my thought to chase the rogue process was fruitless.

I also have checked the logs (events) on the Windows server where the directories are being created. There is also nothing logged there for the time when the creation occurred. My current investigative path is whether the OS or an application is causing this: since the user reboots the system only occasionally, I shut down her system yesterday as she left, and am watching for creation of the directories this morning, which would indicate (perhaps) some OS function.

Can anyone throw any light on this? I have searched and searched all sorts of sites looking for a solution or hints, and nothing has paid out for me. This doesn't appear to be a 'bad' thing, but now I am curious to learn what is going on.