Created attachment 153805 [details]
testcase

Since 69aa7a6392f2ed5d20483b01c0183a3b0fece0be destroying the window a notebook that just got its last tab dragged out causes BadWindow errors from X. Attached is a testcase for this, when running sync dragging a tab from one of the windows to the other causes an X error

$ gdb --args ./detachtest --sync 
GNU gdb (GDB) 7.0.1-debian
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/sjoerd/source/hacks/detachtest...(no debugging symbols found)...done.
(gdb) r
Starting program: /home/sjoerd/source/hacks/detachtest --sync
[Thread debugging using libthread_db enabled]

Gdk-ERROR **: The program 'detachtest' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadWindow (invalid Window parameter)'.
  (Details: serial 8706 error_code 3 request_code 137 minor_code 6)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
aborting...

Program received signal SIGABRT, Aborted.
0x00007ffff5363f45 in *__GI_raise (sig=<value optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
64      ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
        in ../nptl/sysdeps/unix/sysv/linux/raise.c
(gdb) bt

+ Trace 220571