Sorry but I can't stand and not to post in this thread.
This interesting bug, Andru mentioned above, is really like second picture. Gray penguin (OMFG). I add from myself, that if rendertarget will be transparent and non black (green for example), then penguin will be green too(ZOMGF)!
So Andru knew, but I anyway post my result after modification of sourcecode to avoid this "effect" (thanks Andru for idea):