Background transparency issue when using blitting

[elFlashor]

I'm trying to add a semi-transparent background to the BitmapTextField, but when I'm setting the render mode to BLIT, the color and alpha are not properly displayed if I'm not using a complete solid color :

The background color here is supposed to be 0xCC0000FF (slightly transparent blue), but as you can see it only appears in the top-left corner.

Works perfectly in TILE mode.