Re: How to use transparency?
This looks like a depth buffering issue to me — you start with a white background, draw the thing with the border so that it's composited on the white, then draw the thing behind the thing with the border. Those areas where the border was blended with the original white background will have stored a value in the depth buffer equal to the depth of their plane, so when the object behind is subsequently drawn, its pixels are discarded in that area.
The general rule is to draw transparent objects after opaque objects, usually from back to front. If you're using additive blending then it's often good enough to disable the depth buffer after the opaque draw and draw them in any order.
Ambit Energy, Sales Consultant
St. Louis, Missouri