mtv leaves a zombie after exit

For some time now on -current whenever I run mtv, it leaves a zombie after
it exits:

USER     PID  PPID %CPU %MEM   VSZ  RSS STAT STARTED      TIME COMMAND
doug       0     1  0.0  0.0     0    0 ZW   -         0:00.00  (mtvp)

It runs fine, displays the video fine, but it always leaves a zombie.

I realize that this is not a major issue, and there are other video
solutions available, but I thought this might be a symptom of something
else that's worth investigating.

I have tried it with and without witness/invariants, and with and without
the aj -> malloc.conf link, no change in any combination. On releng_4, mtv
exits cleanly.

If anyone is interested in pursuing this, let me know and I'll gladly
provide more information, test patches, etc.

Doug