Serious error on mspaint (transparency)

hi, I have found an extremely serious bug on Paint, and I surprised that nobody noticed it or did something about it.

Imagine the following situation:
you are drawing something, no matter what, and you are using a white background.
let's call the little drawing "A".
let's say you draw something else on this file, let's call it "B".

suposse you want to select "A" and put it over "B", but you don't want "A" to complete replace/erase "B".
so you turn on trasparent selection ON, where the trasparent color, being the second color selected of your palette is equal to the background.
So, you select "A" with the drawing box, and you move it over "B", and WHATTHISTHING you find that "A" has a white rectangle around it covering part of "B", which will be acceptable if you had the trasparent selection OFF, but this is not the case!
so, you drop "A" in other place.
you select it again, and move it over "B", and TADAN! the white rectangle is no more around it! it's gone!


ok, now imagine that case happening at random situations without apparent reason.

Can you please tell me what's going on? This is driving me mad.

thanks for your attention.

surprise, this happens ONLY, if the images (in this case "A") come from an external editor, in this case, game maker....

and this is what I do to fix it:

first, repaint the background twice.
then select "A" and move it somewhere.
Select "A" again and move it somewhere.
now "A" is fixed.

great, ah?