comint-mode broken in GNU Emacs 21.2.1?

[Vincent Montressor]

I'm having trouble using comint-mode under GNU Emacs 21.2.1:

% emacs -nw -q

        M-x compile

Change compile command to something that accepts interactive input, such as cat:

        C-a C-k cat RET

Go to the end of the compilation buffer and enter comint-mode:

        C-x o M->

        M-x comint-mode

Type something and hit RET:

        hello, world RET

Emacs issues the following error:

        error in process filter: Wrong type argument: markerp, nil

Does anyone know how to fix this?