Hhhm...
the code was only a simple snipped. The original code where the issue occurs is more complex, import scripts, uses inheritance, access C++ objects.
The posted example was very small and tight.
Now I have prepared a better example, consists of serveral files (qml, js). It's similar to original code structure. When I start this example at beginning the memory usage rises fast and much space. After short while its rises slower and less space... but rises continually.
I have tested it with Qt's qmlscene.exe.
Note:
I have tested also on Win10, with Qt 5.4.1, no memory issue!
Strange