Source file not found when calling qul_target_qml_sources in child CMakeLists.txt

When child CMakeLists.txt is included to a project using add_subdirectory() cmake gives error:
CMake Error at C:/Qt_2/QtMCUs/1.8.0/lib/cmake/Qul/AddExecutable.cmake:11 (_add_executable): Cannot find source file: V:/xxxxxxx/guidesktopenvironment/build/CMakeFiles/xxxxxxx.dir/_qul_dummy_xxx_input.h

Build system would work if the top-most CMakeLists.txt calls qul_target_qml_sources() or qul_target_generate_interfaces().

When using these commands in any of the child CMakeFiles, errors like "Source file xxxx not found" are shown.

Way to reproduce:

Open the attached application in Qt Creator with Qt for MCUs version 1.8.0 and run cmake.
-> CMake fails and error is shown.