I use subvolumes under some subdirectories like this (from fstab):
/dev/sdb1  /home/johan/Downloads           btrfs   defaults,nofail,subvol=Downloads           0       1

When I now delete a file in Downloads it ends in ~/Downloads/.Trash-1000/files/ but it is not possible to really delete it. The "empty recycle bin" command does not delete the files in the respective subvolumes. It does not even recognize them, so when only files in subvolumes got deleted the "empty bin" command is greyed out.
This is a major privacy problem because you dont see that deleted files are actually not deleted. It is even impossible to delete them from within nautilus without moving them out of the subvolume, because they are moved/copied to the same folder again.