qmake generates wrong relative depedency paths to qt includes

The attached project qtabl2.zip is a most simple test project, created with QtCreator in directory C:\Projects\qtabl2 (see Project_root.png).
Qt 6.7.2 is installed in the default directory C:\Qt (see InstallDir.png).

When I run qmake (either from creator: QMake_Creator.png or command line: QMake_CmdLine.png, qmakeV.log), the resulting Makefile.Debug (see zip) contains such entries:

debug\moc_mainwindow.cpp: ..\..\mainwindow.h \
        ..\..\..\..\..\..\Qt\6.7.2\msvc2019_64\include\QtWidgets\QMainWindow \
        ..\..\..\..\..\..\Qt\6.7.2\msvc2019_64\include\QtWidgets\qmainwindow.h \
        ..\..\..\..\..\..\Qt\6.7.2\msvc2019_64\include\QtWidgets\qtwidgetsglobal.h \
        ..\..\..\..\..\..\Qt\6.7.2\msvc2019_64\include\QtGui\qtguiglobal.h \

The path to the Qt-Includes is wrong (2 ".." too much). Correct would be 
        ..\..\..\..\Qt\6.7.2\msvc2019_64\include\QtWidgets\QMainWindow \
        or
        C:\Qt\6.7.2\msvc2019_64\include\QtWidgets\QMainWindow \

Therefore, when trying to compile I get this error message: 
:-1: Fehler: dependent '..\..\..\..\..\..\Qt\6.7.2\msvc2019_64\include\QtWidgets\QMainWindow' does not exist.
as seen in ErrorMessage_Creator.png and CompileOutput.png

Manually editing Makefile.Debug is a workaround.
For unknown reason, I observed this problem only on some PCs (but there 100% reproducable).