C++ signal > QML slot = ReferenceError (Qt5.12.3)

Hi all,

I am sending signals from C++ and receive them in slots in QML. I am sending to parameters with these signals. Now I get a reference error, that is telling me that this variable (parameter of my signal) is not defined.
 

Here is a minimal example to demonstrate the problem:

link to example

When I start the application out of Qt Creator via "Start debugging" the rectangle keeps blue and I get the error "ReferenceError: name is not defined".
If I start the application via "Run" the rectangle gets red and I get no errors.

I am using Qt5.12.3. (Before I used Qt5.9.)
I am developing on Ubuntu and crosscompiling for Raspberry Pi 3.

I was confirmed that this problem also exists with other platforms. But always in connection with Qt5.12.3.

Does anyone how to solve or workaround this problem?