Thank you,
For external media, I try to unmount, to log out, to log in, to re-mount, to
restart and many other combinations, but nothing worked.
And it was not the first time that I changed the uid.
I had already done this with Ubuntu 12.04.1 LTS 64 bits, and I had not
encountered this bug.
This is the documented behaviour of changing a user's uid with the
usermod(8) tool:
The user's mailbox, and any files which the user owns and
which are located in the user's home directory will have
the file user ID changed automatically.
The ownership
