Hello Martin,

The summary conclusion is that Problem 3 exists both with and without GTK.

The results are somewhat fascinating because of the differences in
performance, which, of course, you cannot see.  Sometimes problem 3 is
easy to see, sometimes it takes several frame creations and deletions.
There is one result where running over the network improves performance!
Running over the network is included because the results, and what I see,
make it hard to avoid speculating that timing/race conditions are at the
root of problem 3.

Here is some detail.  Computer Mneme and Erota run Linux Mint 18.1,
computer Thalia runs Trisquel 7.  I run emacs on all three, sometimes over
my small network.

A "No" entry for problem 3 really means "Not Yet"; but I have tried many
times to generate the problem.

Sometimes it is possible to see the separation of the emacs frame and the
WM window.  There can be a short period before the two coalesce
(flashing), or the two may stay separated.

Version Run     Toolkit  Display  Problem3
25.1    Mneme   GTK3     Mneme    Yes
                GTK3     Thalia   No       This is a surprising result,
                                           given the above; it can be
                                           viewed as a performance
                                           improvement.
                         Erota    Yes      Yes, but very rare.

25.1    Thalia  No       Thalia   Yes      Yes, but rare.
                         Mneme    Yes    
26.0.50 Thalia  No       Thalia   Yes
                         Mneme    Yes      This shows both short period
                                           and permanent frame separation.

25.1    Erota   No       Erota    Yes
                         Mneme    Yes
26.0.50 Erota   GTK3     Erota    No
                         Mneme    No



==========================================================================
==========================================================================

Mneme runs 25.1

It was created by GNU Emacs configure 25.1, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure 

## --------- ##
## Platform. ##
## --------- ##

hostname = Mneme
uname -m = x86_64
uname -r = 4.4.0-53-generic
uname -s = Linux
uname -v = #74-Ubuntu SMP Fri Dec 2 15:59:10 UTC 2016

skip ....

#define EMACS_CONFIG_FEATURES "XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS
 NOTIFY FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11"

configure: exit 0

==========================================================================
==========================================================================

Thalia runs 25.1 and 26.0.50

It was created by GNU Emacs configure 25.1, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure --with-x-toolkit=no

## --------- ##
## Platform. ##
## --------- ##

hostname = Thalia
uname -m = x86_64
uname -r = 3.13.0-113-lowlatency
uname -s = Linux
uname -v = #160+7.0trisquel2 SMP PREEMPT Thu Mar 16 13:56:41 UTC 2017

skip ....

#define EMACS_CONFIG_FEATURES "XPM JPEG TIFF GIF PNG SOUND GSETTINGS
 NOTIFY ACL GNUTLS FREETYPE XFT ZLIB X11"

configure: exit 0

==========================================================================

It was created by GNU Emacs configure 26.0.50, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure --without-makeinfo --with-x-toolkit=no

## --------- ##
## Platform. ##
## --------- ##

hostname = Thalia
uname -m = x86_64
uname -r = 3.13.0-113-lowlatency
uname -s = Linux
uname -v = #160+7.0trisquel2 SMP PREEMPT Thu Mar 16 13:56:41 UTC 2017

skip ....

#define EMACS_CONFIG_FEATURES "XPM JPEG TIFF GIF PNG SOUND GSETTINGS
 NOTIFY ACL GNUTLS FREETYPE XFT ZLIB X11"

configure: exit 0

==========================================================================
==========================================================================

Erota runs 25.1 and 26.0.50

It was created by GNU Emacs configure 25.1, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure --with-x-toolkit=no

## --------- ##
## Platform. ##
## --------- ##

hostname = Erota
uname -m = x86_64
uname -r = 4.4.0-53-generic
uname -s = Linux
uname -v = #74-Ubuntu SMP Fri Dec 2 15:59:10 UTC 2016

skip ....

#define EMACS_CONFIG_FEATURES "XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS
 NOTIFY GNUTLS FREETYPE XFT ZLIB X11"

configure: exit 0

==========================================================================

It was created by GNU Emacs configure 26.0.50, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure --without-makeinfo

## --------- ##
## Platform. ##
## --------- ##

hostname = Erota
uname -m = x86_64
uname -r = 4.4.0-53-generic
uname -s = Linux
uname -v = #74-Ubuntu SMP Fri Dec 2 15:59:10 UTC 2016

skip ....

#define EMACS_CONFIG_FEATURES "XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS
 NOTIFY GNUTLS FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11"

configure: exit 0

==========================================================================
==========================================================================