[pygame] blitting from-to surface with per-pixel alpha doesn't work...

["D. Gyimesi" <dgyimesi@xxxxxxxxx>]

Dear List,

In the pygame documentation one can find the following:
'Surface alphas can be mixed with colorkeys, but an image with per pixel
alphas cannot use the other modes.'

I can interpret this like one can blit pixel data from any number of
surfaces to another with "only" one restriction: all of the surfaces'
transparency must be set to per-pixel alpha.

So, my problem is the following:
I have four surfaces: screen, background, tank and its parts.
The order of blitting: screen<-background and in another cycle
screen<-tank<-parts. All surfaces are having per-pixel-data of course.

Despite of this, the result in the tank surface (the surface I blit into
the parts) draws a strange black 'belt' around the parts, but other
transparent areas of the surfaces are showing up well.

I know it's a little hard to imagine, but did anyone meet a problem
similar to this?

Thank you, and sorry for my english!