KMountPoint doesn't determine the correct mount point, if there are bind mounts. This breaks the Trash handling, files from other devices are moved to the home directory trash folder instead of the trash folder on the other device.

dd if=/dev/zero of=/tmp/test-disk1 bs=1024 count=10000
dd if=/dev/zero of=/tmp/test-disk2 bs=1024 count=10000
mkfs.ext4 /tmp/test-disk1
mkfs.ext4 /tmp/test-disk2
mkdir /mnt/test-disk1
mkdir /mnt/test-disk2
mount -o loop /tmp/test-disk1 /mnt/test-disk1
mount -o loop /tmp/test-disk2 /mnt/test-disk2
mkdir -p /mnt/test-disk1/aaa
mkdir -p /mnt/test-disk2/aaa/bbb
touch /mnt/test-disk2/aaa/bbb/file
mount --bind /mnt/test-disk2/aaa/bbb /mnt/test-disk1/aaa



Stat:

# stat /mnt/test-disk1
  File: /mnt/test-disk1
  Size: 1024            Blocks: 2          IO Block: 1024   directory
Device: 701h/1793d      Inode: 2           Links: 4

# stat /mnt/test-disk2
  File: /mnt/test-disk2
  Size: 1024            Blocks: 2          IO Block: 1024   directory
Device: 702h/1794d      Inode: 2           Links: 4

# stat /mnt/test-disk1/aaa/file
  File: /mnt/test-disk1/aaa/file
  Size: 0               Blocks: 0          IO Block: 1024   regular empty file
Device: 702h/1794d      Inode: 13          Links: 1


------------------------------------------------------
KMountPoint::currentMountPoints():

#include <QDebug>
#include <KMountPoint>

int main() {
    const QString origPath = "/mnt/test-disk1/aaa/file";
    KMountPoint::Ptr mp = KMountPoint::currentMountPoints().findByPath(origPath);
    qDebug() << mp->mountPoint();
}
-------------------------------------------------------

Which returns: "/mnt/test-disk1/aaa", while the file resides on test-disk2.

People complaining about Trash not working correctly:
https://www.reddit.com/r/kde/comments/59cefq/are_there_options_to_manage_how_the_trash_is/