MATLAB: Graphic “ghost”

axisfillimage

I'm creating a object shape with 'fill' and then updating it's position on the screen with 'set'.
When I also use 'image' to insert bit mapped graphics, I think a bug appears.
pseudo code:
a=fill([x1,y1],...);
set(a,[x2,y2],...);
set(a,[x3,y3],...);
set(a,[x4,y4],...);
set(a,[x5,y5],...);
b=image(rand(20)*100,'AlphaData',0.5*ones(20))
set(a,[x6,y6],...);
set(a,[x7,y7],...);
set(a,[x8,y8],...);
set(a,[x9,y9],...);
delete(b);
% at this moment, and only briefly for about 0.1s(even with a pause after), the initial 'fill' graphic will appear at [x5,y5], the position where the 'image' was inserted on the axis. THIS ONLY HAPPENS if the 'image' have the 'AlphaData' channel set…
Is this a confirmed bug or am I doing something wrong?
Regards, Nuno
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