[REG 5.9.4 -> 5.9.5] Rendering of transparent QML items broken on i.MX6

Image, QQuickPaintedItem and maybe others are drawn opaque when they should be transparent.

When testing the 5.9.5 RC from the meta-qt5 repository, we notice broken rendering of our QQuickWidget based application. It seems that, while z-order is preserved, Items are not transparent any more. For example, rendering a QML Image with a transparent PNG file as source will draw the background colour over previous items, instead of showing through.

Qt 5.9.4 and before are working without issues.