[Bug] Window mapping/unmapping problem

[Wesley Merkel]

When using qjackctl (http://qjackctl.sourceforge.net/), some of the
sub-windows of the program don't re-show after being opened again. For
example, if you open the Connections window by clicking the "Connect"
button, close it, then re-open it, then window does not re-appear. Here
is an animation of this: (http://imgur.com/PGobhVh.gif). Although I am
using a custom settings in the animation, I assure you that the bug
still exists when using the default autostart settings. I should also
add that if I close the main qjackctl window and restart the
application, the bug "resets". The windows will appear again, but only
once.

A narrowed down the commit which introduced the bug. It is 33a9258,
which is somewhere between v0.5.3 and v0.6.0. I also ran `xwininfo -root
-all` a few times to figure out what was going on. The results are
attached in "xwininfos.tar.gz", and are organized accordingly:

xwininfo ran on the first commit with the bug (33a9258):
    buggy/*/*
xwininfo ran on the last commit without the bug (33a9258~):
    clean/*/*

xwininfo ran during various times during the use of the "Connections"
window, a window in which the bug is present:
    */connections/*
xwininfo ran during various times during the use of the "Setup" window,
a window in which the bug is not present:
    */setup/*

xwininfo ran right after starting qjackctl:
    */*/1-before
xwininfo ran right after opening the window in question:
    */*/2-opened
xwininfo ran right after closing the window:
    */*/3-closed

I did not include the output of xwininfo after the re-opening of the
window failed, because it does not change from the '3-closed' state,
which seems to be the problem.

If you want to see the bug with your own eyes, you can download qjackctl
and try opening the aforementioned windows. You don't need to setup
anything or use any audio hardware to run the application, the bug
exists right out of the box.

I'm trying to fix the bug myself, but I don't know much about X, or the
internals of herbstluftwm, so I am having a little trouble. Any help
would be much appreciated.
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