CONFIG-=depend_includepath breaks build for UI files with promoted widgets

The qmake option CONFIG-=depend_includepath has been proposed as a work around for the 8 times slower qmake times in Qt5 compared to Qt4 (see Bug QTBUG-37252)

We upgraded from Qt 5.9.2 (MinGW 5.3) to Qt 5.12.2 (MinGW 7.3). The build of a large project failed after the upgrade. We could track down the problem to the option CONFIG-=depend_includepath. If we removed this option from the qmake file, the build succeeded. But then the qmake time raised from 1 Minute to 7 Minutes.

The attached test case promotest shows the problem. If the option CONFIG-=depend_includepath is enabled, the build of the Dialog.ui fails because it uses the promoted widget CustomWidget.h.

make -f Makefile.Release
make[1]: Entering directory 'C:/temp/promotest'
make[1]: *** No rule to make target 'promotest/CustomWidget.h', needed by 'ui_Dialog.h'. Stop.
make[1]: Leaving directory 'C:/temp/promotest'
make: *** [Makefile:38: release] Error 2

Only if the option is removed from the qmake file, the project build succeedes. The project builds properly for Qt 5.9.2, so I would say, something is broken