I'm sorry, I didn't get it right.
So something got wrong in converting to png. I don't use png very often, just for screenshots.
I never thought that some problems could emerge.
I don't keep the source & output files [last week I did bmp, too] with me right now, so you will get a correct version tomorrow.
Thanks kusmi for the link, crux is hidden in detail.
[Edit]: I updated the files, read 1st post.