xcb_io.c assertion error following forkpty and raw_input in PyGTK

I am writing a PyGTK application which involves a vte Terminal. I use a forkpty() call to launch a child process in the terminal. When the child process runs a raw_input(), it dies with the message:

python: ../../src/xcb_io.c:242: process_responses: Assertion `(((long) (dpy->last_request_read) - (long) (dpy->request)) <= 0)' failed.

(Actually, the child process seems to survive until there is either a keystroke or mouse movement over the terminal.) The parent process survives. This behavior is on an up-to-date Karmic install. On Jaunty, this error does not occur. The attached file provides a test-case program.

This is the same error message reported in bug #419501. I've reported separately, as it is triggered in quite different circumstances. But if it is the same, please mark this as a duplicate.

[Aside - the submission page asked me to submit this using `ubuntu-bug -p libxcb`. But that failed in two ways: First, it warns that -p is deprecated. Second, it tells me "Package libxcb does not exist", and quits.]