freebsd stable - Aug 2015 - Latest stable (r287104) bash leaves zombies on exit

I updated to stable yesterday, plus updated all my porst to
the latest pecompiled packages, but I am now seeing odd problems
with bash on exit. Sometimes it quits, but leaves a zombie
process... e.g

  PID TT  STAT    TIME COMMAND
44308 v0  IW   0:00.00 -bash (bash)
44312 v0  IW+  0:00.00 /bin/sh /usr/local/bin/startx -listen_tcp
44325 v0  IW+  0:00.00 xinit xterm -listen_tcp -- /usr/local/bin/X :0 -auth /ho
44328 v0  IW   0:00.00 /usr/local/bin/wmaker
44340 v0  S    0:03.35 /usr/local/bin/wmaker --for-real
49101  0- Z+   0:02.73 <defunct>
49314  1- Z+   0:00.17 <defunct>
56068  2  Ss   0:00.01 bash
56498  2  R+   0:00.00 ps
56074  3  Is   0:00.01 bash
56076  3  S+   0:00.00 mail freebsd-stable at freebsd.org
56308  4  Is+  0:00.01 bash

Thats the current 'ps' on this machine. The bash processes are running
inside an xterm, so am not sure if the issue is with bash or the
terminal. Kind of puzzled!

-pete.