glitchy QPixmap drawing on paint area

Hi. I've tried to change only color of existing QPixmap, but use old alpha. I've changed pixels colors with setPixel using old alpha, but when I'm drawing this image everything glitches.

https://dl.dropbox.com/u/44131220/undeletable/scr15.png
https://dl.dropbox.com/u/44131220/undeletable/scr16.png

Code and application visable on screenshots. If I don't change rgb values everything looks good.

Added after 20 minutes:

Ok, i quite don't get it, but rgb value can't be bigger than alpha value. If I use

setPixel(16, 0, 0, 16);

I'm getting 100% red transparent pixel. Just If someone have the same problem ;)