[REG 5.4.1->5.5.0-beta] Angle: shader effect and image with alpha channel in the same window lead to a black box

We have a svg image as a background and an image with OpacityMask on top of it. When running with ANGLE on Qt 5.5.0-beta the masked image is black and the debug log has several D3D11 warnings like

D3D11 WARNING: ID3D11DeviceContext::DrawIndexed: The Pixel Shader unit expects a Sampler to be set at Slot 1, but none is bound. This is perfectly valid, as a NULL Sampler maps to default Sampler state. However, the developer may not want to rely on the defaults. [ EXECUTION WARNING #352: DEVICE_DRAW_SAMPLER_NOT_SET]

The problem is not reproducible with desktop OpenGL nor in Qt 5.4.1. In addition this happens with only some svg images.

Attached example reproduces the problem. Change the Image source to see how it should work.