RawTherapee 5.9 on Windows 10 never remembers window positions and panes

Before filing a proper bug report, I’d like to see whether this is considered a “bug” at all.

I’m using RT 5.9 on Windows 10.

Version: 5.9
Branch: 5.9
Commit: 9b8583988
Commit date: 2022-11-27
Compiler: cc 12.2.0
Processor: generic x86
System: Windows
Bit depth: 64 bits
Gtkmm: V3.24.7
Lensfun: V0.3.3.0
Build type: release
Build flags:  -std=c++11 -ffp-contract=off -mtune=generic -Werror=unused-label -Werror=delete-incomplete -fno-math-errno -Wno-attributes -Wall -Wuninitialized -Wcast-qual -Wno-deprecated-declarations -Wno-unused-result -Wunused-macros -fopenmp -Werror=unknown-pragmas -O3 -DNDEBUG -ftree-vectorize
Link flags:  -mtune=generic
OpenMP support: ON
MMAP support: ON
Build OS: MINGW64_NT-10.0-20348 3.3.6-341.x86_64 x86_64
Build date: Sun, 27 Nov 2022 18:38:56 +0000 UTC
Build epoch: 1669574336
Build UUID: 9d19d210-c668-4aa2-8af6-2d527fd55d1c
Windows 10 Pro
Version: 22H2
Build: 19045.3324

RT never remembers window positions, i.e. the editing window never starts maximized to the screen as I’d very much like it to. And also, very likely connected to that, positions/sizing of panes also resets with every restart of the editor, even when starting a new editing session without closing down the main window.