The spawned process (you appear to have run on Windows, so I'm assuming spawn but that's not so significant) has triggered an unhandled exception.  If the triggering and subsequent sending of the traceback to stderr is synchronous and completes before Python actually kills the process, then the original "one would expect" statement would make sense.  Removing the use of the Queue entirely and substituting the use of a socket to communicate from the child (spawned) process to some distinct listener process results in only a portion of the traceback text being received by the listener (or sometimes little to none of the traceback text).  This suggests that the original premise is false and the expectation inaccurate.