Description:

When I collapse a window (not minimize), and then cycle through, the window switcher dialog appears 
momentarily and then disappears abruptly.  Enough rapid presses causes all of the window manager 
to disappear.

Steps to reproduce:

1. Have a few windows open in the current workspace
2. Collapse one of them
3. Move focus to another window
4. Press Alt+Tab (or whatever combination will cycle windows)


Expected behavior:

The window switching dialog comes up and stays up, allowing multiple presses to cycle through the
active windows.

Observed behavior:

The dialog closes immediately.  Additionally, after multiple rapid presses (possibly requiring a 
second window to be collapsed), observe the following dmesg outputs:

[ 1560.905402] do_trap: 65 callbacks suppressed
[ 1560.905407] traps: xfwm4[1794] trap int3 ip:7fd0c2cb53c5 sp:7fffbe1c69e0 error:0 in libglib-2.0.so.0.5800.1[7fd0c2c7c000+7f000]
[ 1561.582757] traps: xfwm4[20037] trap int3 ip:7f01163db3c5 sp:7fff2d17b2d0 error:0 in libglib-2.0.so.0.5800.1[7f01163a2000+7f000]
[ 1562.274364] traps: xfwm4[20074] trap int3 ip:7fa86115d3c5 sp:7ffe2c7afd40 error:0 in libglib-2.0.so.0.5800.1[7fa861124000+7f000]
[ 1564.446783] traps: xfwm4[20108] trap int3 ip:7f1e513aa3c5 sp:7ffdb06ebbf0 error:0 in libglib-2.0.so.0.5800.1[7f1e51371000+7f000]
[ 1573.317213] traps: xfwm4[20203] trap int3 ip:7ff293b423c5 sp:7ffe16bf2e10 error:0 in libglib-2.0.so.0.5800.1[7ff293b09000+7f000]
[ 1579.448359] traps: xfwm4[20260] trap int3 ip:7fba7906c3c5 sp:7fffa89243e0 error:0 in libglib-2.0.so.0.5800.1[7fba79033000+7f000]

xfwm4 stopped respawning at that point, and while trying to recover it, I also saw these
additional crashes, which may be related (or just could be my plokta-fu):
[ 1637.004361] xfce4-terminal[2236]: segfault at 90 ip 00007fc8dddcda1a sp 00007ffe28e87c20 error 4 in libgdk-3.so.0.2400.1[7fc8ddd93000+7d000]
[ 1637.004367] Code: 41 0f 10 4f 60 4c 89 75 38 f2 0f 5e c8 f2 0f 11 4d 48 e8 19 94 fd ff 4c 89 f7 e8 61 18 fd ff 48 89 ef 48 89 c6 e8 36 a0 fd ff <49> 8b b5 90 00 00 00 48 89 ef e8 b7 a0 fd ff 49 8d 97 b8 00 00 00 
[ 1637.033868] xfdesktop[1806]: segfault at 90 ip 00007f997f249a1a sp 00007ffca348afd0 error 4 in libgdk-3.so.0.2400.1[7f997f20f000+7d000]
[ 1637.033881] Code: 41 0f 10 4f 60 4c 89 75 38 f2 0f 5e c8 f2 0f 11 4d 48 e8 19 94 fd ff 4c 89 f7 e8 61 18 fd ff 48 89 ef 48 89 c6 e8 36 a0 fd ff <49> 8b b5 90 00 00 00 48 89 ef e8 b7 a0 fd ff 49 8d 97 b8 00 00 00 
[ 1637.044528] xfce4-panel[1797]: segfault at 90 ip 00007f0f64caea1a sp 00007fffd7812d00 error 4 in libgdk-3.so.0.2400.1[7f0f64c74000+7d000]
[ 1637.044534] Code: 41 0f 10 4f 60 4c 89 75 38 f2 0f 5e c8 f2 0f 11 4d 48 e8 19 94 fd ff 4c 89 f7 e8 61 18 fd ff 48 89 ef 48 89 c6 e8 36 a0 fd ff <49> 8b b5 90 00 00 00 48 89 ef e8 b7 a0 fd ff 49 8d 97 b8 00 00 00 
[ 1657.813213] traps: xfwm4[20525] trap int3 ip:7f50ca2cd3c5 sp:7ffe6e2bdf00 error:0 in libglib-2.0.so.0.5800.1[7f50ca294000+7f000]