reconfguration fails in qtpositioning after config change

This bug haunts me for the last five months, but only now did I understand what I did to provoke it:

Environment:

• Ubuntu 20.04
• Clang 10.0.0 (also observed with self-compiled GCC 11.2)
• cmake 3.21.2 (from Qt installation)
• cat config.opt

  -opensource
  -confirm-license
  -release
  -force-debug-info
  -separate-debug-info
  -c++std
  c++20
  -developer-build
  -nomake
  examples
  --webengine-jumbo-build=20
  -webengine-proprietary-codecs
  -sctp
  -platform
  linux-clang-libc++
  

Given:

• a qt5.git checkout, configured and (at least partially built, I guess) with config.opt as above
• in an out-of-source build (srcdir: _/Qt/qt5, builddir: /Qt/qt5-build-clang)

When:

• changing config.opt to exclude -developer-build and
• rm CMakeCache.txt and
• running ../qt5/configure -redo

Then:

• configuration fails with the following cryptic message

  Configuring 'qtpositioning'
  CMake Error: The source "/home/marc/Qt/qt5/qtpositioning/src/positioning/../../config.tests/winrt/CMakeLists.txt" does not match the source "/home/marc/Qt/qt5/qtlocation/src/positioning/../../config.tests/winrt/CMakeLists.txt" used to generate cache.  Re-run cmake with a different source directory.
  CMake Error at qtbase/cmake/QtFeature.cmake:908 (try_compile):
    Failed to configure test project build system.
  Call Stack (most recent call first):
    qtpositioning/src/positioning/configure.cmake:11 (qt_config_compile_test)
    qtbase/cmake/QtModuleHelpers.cmake:573 (include)
    qtpositioning/src/positioning/CMakeLists.txt:7 (qt_internal_add_module)
  
  
  -- Configuring incomplete, errors occurred!
  See also "/home/marc/Qt/qt5-build-clang/CMakeFiles/CMakeOutput.log".
  See also "/home/marc/Qt/qt5-build-clang/CMakeFiles/CMakeError.log".
  CMake Error at /home/marc/Qt/qt5/qtbase/cmake/QtProcessConfigureArgs.cmake:963 (message):
    CMake exited with code 1.
  

• and rm CMakeCache.txt doesn't fix it
• and rm -rf qtpositioning doesn't fix it
• and rm -rf qtlocation doesn't fix it
• only removing the whole build-dir and starting from scratch helps

Expected:

• reconfiguration does not fail