Xpraversion and Xprarelease are only set when explicitely selecting --xpra

[jd666]

Warning messages due to implicit selection of xpra:

$ xpra --version
xpra v3.0.6-r25177
$ x11docker --podman --desktop --size 1400x900 x11docker/mate
x11docker note: Option --podman: experimental only.

x11docker note: Using X server option --xpra

x11docker note: Your xpra version  is out of date. It is
  recommended to install at least xpra v1.0. Look at:  www.xpra.org

x11docker note: Your xpra version does not support desktop mode.
  Please use another X server option like --xephyr or --nxagent.

x11docker note: Xpra desktop mode works best since xpra v2.2-r17117.
  You have installed lower version xpra .
  It is recommended to use --xephyr or --nxagent instead.
  Rendering issues can be reduced disabling OpenGL in Xpra tray icon. Screen
  size issues can be avoided with non-integer scaling (e.g. --scale=1.01).
...

[mviereck]

Thank you for the report! I am looking at this.

[mviereck]

The bug is fixed now. Thanks again!