Regression (Qt >= 5.12): Memory leak when passing QImage through QML

To be able to trigger the update of a live image from our sensor via QML, we use a QImage  property in the data source class and in the display class (QQuickPaintedItem). Whenever the QML Gui requests an update, the image is updated via assignment. See a minimal example attached.

This worked well and efficiently with all Qt versions earlier than 5.12.x (latest working version is Qt 5.11.3). With Qt >= 5.12 a memory leak was introduced. By the amount of memory leaked per request it is clear, that the image is copied somewhere instead of implicitly shared (or not released).

It might be that our approach is wrong, but it it is still weird that older Qt versions worked.

Tested on Windows 10 only.