: I posted a query about this already, and the only reply I got was
: someone saying "There's a process using the virtual terminal", but
: that doesn't appear to be the case.
Nevertheless I would conjecture that it is true.
There are many ways a process could use a tty directly or indirectly.
Try to also make /dev/tty1[0-9] and watch what X does.
It will cycle.
(If not then there would be a bug in tty close - but nobody sees
such a bug.)