xdg-open (OpenURI portal) is leaving files open

[sophie-h]

Minimal example using flatpak-builder --run for the call inside flatpak

flatpak $ xdg-open ~/test/dir
host $ lsof -f +D ~/test/
COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF     NODE NAME
xdg-deskt 4881 sophie   12u   DIR  253,1     4096 15082214 /home/sophie/test/dir

This also happens using glibs g_app_info_launch_default_for_uri() in a program started via flatpak run. The path is still open after exiting the flatpak.

I am using fusermount inside the flatpak and the showing the directory to the user via the OpenURI portal. However, I can't umount the fuse mount when shutting the program down ("Device or resource busy.") I would also be grateful if there is an idea for a workaround while this problem with the portal exists. Would it be possible to bypass the sandbox and run something like xdg-open on the host?