I've eliminated eCryptfs from the equation and can still trigger the BUG.
I set up the two schroot sessions and rebooted, as described in comment #9. Then I logged in as a user without an encrypted home and ran the following commands:
$ mkdir t $ sudo mount -t tmpfs tmpfs t
That triggered the same BUG in propagate_one().
I've eliminated eCryptfs from the equation and can still trigger the BUG.
I set up the two schroot sessions and rebooted, as described in comment #9. Then I logged in as a user without an encrypted home and ran the following commands:
$ mkdir t
$ sudo mount -t tmpfs tmpfs t
That triggered the same BUG in propagate_one().