The org.apache.commons.vfs2.cache.DefaultFilesCache does not remove the filesystem specific cache if a filesystem gets cleared. This leads to the problem that instances if the FileSystem kept alive after the FileProvider has closed the filesystem. This is not so much a problem for a smaller number of filesystems configured for a prefix, but it is a problem for layered or virtual filesystems which get created and destroyed. (See also
VFS-544). The more advanced filesystem caches support clearing the keys (but have other races I think).
The behaviour is somewhat documented "lifetime of the FileSystemManager", but I don't think it is expected or required.