Discrepancy in behaviour of docker run-with-immediate-attach vs run-and-then-attach

gistfile1.txt

# Normal run, without -d.
# Container prompt appears immediately; after exiting, system prompt appears on new line.

$ docker run -i -t ubuntu bash
root@0b3fa3041e3f:/# exit
exit
$

# Now run with -d and *then* attach.
# Container prompt doesn't appear until I hit Enter; after exiting, system prompt appears on same line.

$ docker run -i -t -d ubuntu bash
9c1bcb6ed547
$ docker attach 9c1bcb6ed547
<PRESS ENTER>
root@9c1bcb6ed547:/# exit
exit$