Some additional Information which probably helps to find the root cause: The very same beheaviour (as in Jessie) is still shown in Stretch. I already tried to assign that bug to package "mount", but this was not accepted. The corresponding bug report demonstrates some more possibilities of "how you can workaroung" this faulty beheaviour. See here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=788547#12