Hi,
I have found out fus is storing cached metadata in ~/.cache/fus. This is quite OK, but it should try to remove them once it finishes using it. I understand that in case of crash or some unpredictable issue, the metadata can stay there, but I think generally it should remove it.
So far I have to add following cronjob to clean that directory to composer machine we use:
find ~/.cache/fus -type f -mtime +1 -exec rm {} ;