gio trash doesn't recognize existing trash directory in non-fs-root mount

gio trash doesn't recognize existing trash directory in non-fs-root mount:
The following shell commands show the existing correct trash folder (/sw/mount1/.Trash/1024) and the last line the error message produced by the broken gio trash command:

% mount | grep sdc6
/dev/sdc6 on /sw/mount1 type ext4 (rw,relatime)

% ls -ld /sw/mount1/.Trash/
drwxrwxrwt 3 root root 4096 22. Feb 22:51 /sw/mount1/.Trash/

% ls -l /sw/mount1/.Trash/
drwx------ 4 user1 users 4096 12. Mai 22:12 1024

% cd /sw/mount1/subdir/
% gio trash blablabla.txt
gio: file:///sw/mount1/subdir/blablabla.txt: Unable to find or create trash directory /sw/mount1/.Trash/1024 to trash /sw/mount1/subdir/blablabla.txt

Judging from the code (but I'm new to the glib codebase) this bug was introduced by commit 7f2af262 and activated by commit c983ded0