WebDav/Webdisk password resets

We have a very strange issue where the password (I assume) for some specific accounts keeps... changing, I guess. All Web Disk accounts that have this issue have the same thing in common: Their "Directory" is configured as "/". Each Web Disk accounts is mapped as a network drive in Windows. When trying to access the network drive, username/password combination is incorrect. We reset the password through cPanel and try again - success. Then a few days later, the username/password combination is incorrect again. Nothing has been changed. Go to cPanel, change the password to the exact same thing as before... Success again. Any idea what could be causing this?