mpv creates weirdly named directories in location of the video (on nfs mount) when taking screenshots

[q66]

FreeBSD 11-CURRENT
mpv 0.16

When playing videos from my NAS (via NFS mount) on FreeBSD (NAS is also running FreeBSD, with ZFS on the server side) and I take a screenshot (with ctrl+s as usual) it creates the screenshot in my home directory but also creates a directory usually called "ZZZZZZZZZZ" (the number of Zs varies) where the video is located. Sometimes additional garbage characters are inserted into the directory name (invalid unicode sequences, as filenames use UTF-8). Other than this, the screenshots seem to be correct etc. and I can just delete those dirs with normal rmdir command.