I just ran into another problem using draw_quad and bmap_rendertarget.
It seems like draw_quad performs incorrect alphablending:



In this screenshot I'm drawing a title bar with a soft shadow onto an orange (100% opaque) bmap.
It should look like the top image but the bottom one is the result.

As you can see, the background (in this case a blue-green checker pattern) is clearly visible which means that draw_quad has lowered the alpha values of these pixels.

Sadly, this behaviour renders alphablending useless and causes me a lot of trouble.