QImage.scale(with, height) automaticaly convert Format_ARGB32 images to Format_ARGB32_Premultiplied

when using scale on image with alpha value, this has a strange impact :

i have an image with transparent border :
image1 : 0 = rgba(255,255,255,0), 1 = rgba(255,255,255,255)
01110
01110

when i scale the image1 with a shorter width i get border with gray
I assumed that the scale is performed on premultiplied values so 0 and 1 are merged.

The problem may be that with premultiplied values all 0 is considered as black, then black + white becomes gray, but this is not the correct behavior!

transparent + white should produce (255,255,255,126)

I hope i have been enough clear.