Terminal locked when spawning a new tty frame

[Alex Bennée]

Hi,

On the current master I seem to be running into a semi-intermittent
problem spawning terminal frames. I'm usually running an emacs --daemon
with a GUI frame but from time to time I shell into my box and issue a:

  emacsclient -a '' -t

The frame gets created and comes up on the *scratch* buffer but it's not
responsive to keyboard input. I end up having to kill the emacsclient or
kill-window'ing my tmux frame it's in. If I SIGUSR2 the main emacs pid I
get the message:

  "Terminal 5 is locked, cannot read from it"

So far SO points out that this is because something is trying to read
the minibuffer on another tty although I'm not sure which tty this might
be as I've both a) left the GUI frame alone and b) ensured I've closed
any GUI frames before working remotely.

This doesn't happen all the time because after killing emacs and
restarting the daemon I have a working session again and can launch GUI
frames when I get back home.

So any ideas on how I can debug this next time it occurs?

--
Alex Bennée