This also explains why I had Applications menu : incomplete keyboard browsing & no recent category where I could not open files from trash.
It’s still true today : using trash-applet I’m able to open files from [user id = 1000]/.local/share/Trash but not those from /media/DATA/.Trash-1000
As a workaround should I link for each user ~/.local/share/Trash to each matching /media/DATA/Trash-* ?
→ auto-answer, not what I expected as this just reverses the situation regarding partitions : what comes from /media/DATA is now handled by trash-applet but not what comes from / partition. So in my context it’s a bit better since only the root of /home/$USER is really located on /
→ but confirms only ~/local/share/Trash is taken care by trash-applet, as long as files-put-on-deletion share the same partition
→ now if I try to delete something from the root of /home/$USER, I have a warning « unable to put it in trash - do you want to definitely delete ? »