WebDAV and Network: Folders are displayed as exec Unix Files

I have a problems with some folders accessed by WebDav or in the Network. From times to times some folders are not displayed as a folder anymore, but as an exec Unix File. I don't know when this happens. This Files cannot be opened as a folder anymore. By having a look on the folders on the NAS directly (Synology), there is no error.

Do I have a wrong configuration on may Mac (Mountain Lion) and how can I solve this problem?