Q: Strange behavior creating a dockable dialog using PythonScript plugin

[Ekopalypse]

Description of the Question

Doackable dialogs created with Python and the PythonScript plugin behave strangely because they are either not "themed" or embedded controls "visually" disappear unless you hover over them.
As far as I know, a docked dialog is automatically "themed", which can be seen even if the controls are not visible, but this is not the case if I do a print output inside the WM_PAINT, but then the controls are visible !??.
The test dialog contains only 2 standard buttons, no user specific controls.

Does anyone have any idea why this is happening?

Debug Information

Notepad++ v8.5.4 (64-bit)
Build time : Jun 17 2023 - 20:42:45
Path : D:\Tests\npp\854\x64\notepad++.exe
Command Line :
Admin mode : OFF
Local Conf mode : OFF
Cloud Config : OFF
OS Name : Windows 10 Pro (64-bit)
OS Version : 22H2
OS Build : 19045.2728
Current ANSI codepage : 1252
Plugins :
mimeTools (2.9)
NppConverter (4.5)
NppExport (0.4)
PythonScript (3.0.16)