Trying to type & with de keyboard layout results in K

[Voros-Roka]

Describe the bug
When trying to type &, shift+6 with a de keyboard layout on client, K is inserted instead.

To Reproduce
Steps to reproduce the behavior:

1. server command: xpra start :0 --uid=1000 --gid=1000 --mdns=no --exit-with-client=no --exit-with-children=no --exit-with-windows=no --daemon=no --mmap=/sys/devices/pci0000:00/0000:00:08.0/resource2_wc --bind-vsock=auto:2000
2. client command: XPRA_USE_NATIVE_TRAY=0 xpra attach vsock://4:2000 --mmap=/dev/shm/my-ivshmem --border=red,8 --opengl=no --sharing=yes
3. Pressing shift+6 to type & with de keyboard layout on server and client

System Information (please complete the following information):

• Server OS: Artix Linux
• Client OS: Artix Linux
• Xpra Server Version: commit gce124c6415 from master branch
• Xpra Client Version: commit g75d2762385 from v6.2.x branch

Additional context
The server runs with xdummy inside a qemu vm. LightDM is the display manager and AwesomeWM the window manager both on server and client. There is no compositing involved. xpra is set to keyboard layout auto in the menu. While testing commit ce124c6 (on server) for issue #4403 i noticed that when i am trying to type & (shift+6) with a de keyboard layout (setxkbmap de on client) i get a K instead. This did definitely not happen with 75d2762 or any previous version as server. I tried ce124c6 and 75d2762 as clients but there was no difference, i still got K instead of &. xpra toolbox -> keyboard shows the following for pressing the 6 without shift:

down 6                            '6'   54        15     0 0    2
up   6                            '6'   54        15     0 0    2

and for shift+6:

down Shift_L                      ''    65505     50     0 0    S
down K                            'K'   75        45     0 0    S, 2
up   K                            'K'   75        45     0 0    S, 2

That got me curious and i tried different combinations that resulted in the following table (N/A means that while pressing the key nothing happened):

setxkbmap client	setxkbmap server	shift+6 expected	shift+6 actual	shift+7 expected	shift+7 actual
de	de	&	K	/	/
de	us	&	K	/	&
us	us	^	^	&	K
us	de	^	N/A	&	K

Something between commit 75d2762 and ce124c6 changed that leads to that behavior. Even if we disregard mismatched layouts between server and client there is definitly something wrong. I did not notice any problems with other keys. Sadly i am currently not able to provide more information then that, but as soon as i am able to what can i provide to help with debugging?

[totaam]

Likely a duplicate of #4396

The commit has been reverted in v6.2.x

I'm trying to find a better solution for git master.