QML modules' don't work if defined in subdirectory of target (CMake API)

Hello,
this issue occurs with the CMake API for QML modules. I've encountered the error when trying to create a QML module in the subdirectory of the module's target. Here are the steps to reproduce the issue:

First, I've created a new project with the following directory structure:

Project
 +-- CMakeLists.txt (root)
 +-- main.cpp
 +-- gui
    +-- CMakeLists.txt (child)
    +-- Main.qml

Inside the root CMakeLists, I've called qt_standard_project_setup and created a new executable (app):
qt_add_executable(app main.cpp)

Then I've created a new QML module (example) on target app inside the child CMakeLists:
qt_add_qml_module(app
 URI example
 QML_FILES Main.qml
)

When I run CMake, it fails on step Automatic QML type registration for target app with the following output:

FAILED: app_qmltyperegistrations.cpp qml/example/app.qmltypes build/app_qmltyperegistrations.cpp build/qml/example/app.qmltypes 
cd build/qml && /usr/lib/qt6/qmltyperegistrar --generate-qmltypes=build/qml/example/app.qmltypes --import-name=example --major-version=254 --minor-version=254 @build/qmltypes/app_foreign_types.txt -o build/app_qmltyperegistrations.cpp build/meta_types/qt6app_debug_metatypes.json && /usr/bin/cmake -E make_directory build/.generated && /usr/bin/cmake -E touch build/.generated/app.qmltypes
Error 5 while parsing build/meta_types/qt6app_debug_metatypes.json: illegal value
ninja: build stopped: subcommand failed.

I've simplified the build directory path to build and bolded the actual error. The qt6app_debug_metatypes.json file is empty (size=0).

If I instead move the Main.qml file to root directory and move the QML module declaration to root CMakeLists, everything works as intended. Interestingly, if I then go back to the erroneous directory structure, CMake works correctly until I remove the build folder, after which it will again raise the error described above.

Creating a new target using qt_add_library, making it the QML module target and linking the library to root executable works, but it isn't what I'm aiming for.

I am using CMake 3.28.1 and Qt 6.6.1 on Linux (Manjaro).