Multiple separate X11 screens setup (Zaphod, no Xinerama) fails

[Manfred-Knick]

My setup:
2 graphic "card"s with 1+3=4 monitors
= four separate X11 screens
( c.f. xorg.conf.d -> Attachment ).

Layout "Single":
works like a charm.

Layout "Four":
Only on the fist screen a rudimentary desktop appears,
ending in a message like "failed too often".
The other three remain black.
In principle, all four X11 screens get addressed;
at least the "X" sign mouse cursor flows over the rest of the four.

Cross-Check:
Plain X works with (c)twm, as well as fluxbox, xfce, ... on all four screens.

Question:
Perhaps this may be due to lxqt-session depending upon qtdbus,
thus inheriting dbus' limiting factor being head agnostic ?
(BTW: KDE suffers the same root cause.)

[Manfred-Knick]

Device-01.intel.conf.TXT
Device-11.nvidia.conf.TXT
Monitor.conf.TXT
Screen.conf.TXT

Files.conf.TXT
InputDevice_Keyboard.conf.TXT
InputDevice_Mouse.conf.TXT
ServerFlags.conf.TXT

ServerLayout.conf.TXT

[Manfred-Knick]

$ uname -a
Linux . . . 4.3.0-gentoo . . . x86_64 Intel(R) Xeon(R) CPU E3-1276 v3 . . .

$ equery list lxqt-base/*
[IP-] [ ] lxqt-base/liblxqt-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-about-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-common-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-config-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-globalkeys-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-meta-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-notificationd-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-panel-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-policykit-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-qtplugin-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-runner-0.10.0:0
[IP-] [ ] lxqt-base/lxqt-session-0.10.0:0

[Manfred-Knick]

$ equery g --depth=20 lxqt-session | grep dbus | sort
. . . [ extract ] . . .
[ 18] dev-qt/qtdbus-4.8.6-r1
[ 18] dev-qt/qtdbus-5.4.2
[ 19] sys-apps/dbus-1.8.20

[Manfred-Knick]

Perhaps related:
"Improve external monitor handling." #239
"lxqt-panel should respect the xdg-way of reading configurations" #385

[Manfred-Knick]

Just tried to test against current git sources from qt overlay ( "layman -a qt" )
( referring to git://anongit.gentoo.org/proj/qt.git ) ;
unfortunately, packages fail during 'configure' phase already.