It looks like the panel is still dropping zombies, but now when external plugins
are removed normally.  My guess is either you aren't ignoring SIGCHLD, or you're
not reaping the zombie processes properly...  I'm not sure if ignoring SIGCHLD
is the right idea, though, since it may bring back the problem where abnormal
panel termination will leave the plugins running =p.  So I guess you just have
to have a SIGCHLD handler that calls waitpid() on the plugin process if
something's removed.