How to grab the backbuffer *with* alpha

BlitzMax Forums/BlitzMax Programming/How to grab the backbuffer *with* alpha

glmax2d.bmx: line 361
Method Graphics( width,height,depth,hertz )
		Local bgl_flags=BGL_BACKBUFFER|BGL_ALPHABUFFER
		'Local bgl_flags=BGL_BACKBUFFER
....


I'm willing to concede that it could be my graphics card [geforce2 GTS/32m] or something else. If someone can confirm that my sample code above does truly render a tga with the empty space having alpha $00 and preserving the alpha of loaded image, then that would be good enough for me.