FileZilla Server 0.8.6a has been released. It contains a workaround for a bug in the Windows api function CreateDirectory. Due to the bug it is possible to create directories which names end with one or more dots. Those directories were unaccessible and couldn't be deleted with most programs. FileZilla Server now denies creation of such directories.
Please look into the readme for instructions how to manually remove such directories.
Upgrading to FileZilla Server 0.8.6a is highly recommended.