[REG 5.11.2->5.12.1] winrt: Assert fails in ANGLE

Running the mapviewer example in debug will stop execution shortly after launch, with the indication of an assert failure in libANGLE/renderer/d3d/d3d11/StateManager11.cpp, line 1665:

1663    // Applies the render target surface, depth stencil surface, viewport rectangle and
1664    // scissor rectangle to the renderer
1665    ASSERT(framebuffer && !framebuffer->hasAnyDirtyBit() && framebuffer->cachedComplete());

Running the same example in release will not stop execution but will render text incorrectly:

1. Open the "Provider" menu
2. Move mouse pointer to head of the "MapType" menu
3. All text will now be rendered with boxes overlaid (cf. attached screen captures)

With Qt 5.11.2 the problem does not occur.