Displaying Folder Content within a folder

Hello,

it's a little bit strange to describe this issue.
A customer opens the windows explorer and navigates to a certain folder by double-clicking the upper folders on the right side.
After entering the folder with the name "Aufträge" (german for orders) all files within this _sub_folders are displayed and the folders aren't displayed at all. In the showing list is a column that displays the original path to the file.
When entering the folder again I see the folders within this folder and none of the files.
The most strange behaviour is following: Changing the foldername to "Auftraege" solved the problem. After changing the name back to "Aufträge" the strange behaviour occurs again.
I then thought this must be a problem with the "Umlaut" "ä" and found a folder named "Präsentationen" (german for presentations) but the strange behaviour doesn't occur. Everything was like it should be.

So does anyone had this problem, too? Does anyone solved this problem?
BTW. Customer runs W7 pro 64bit

Thanks
Jens