QImage save to BMP is broken when bytesPerLine != width

I construct an 8-bit indexed QImage around an existing memory buffer, using the constructor that takes bytesPerLine argument. My image has width=6144, bytesPerLine=8192.
Then I call QImage::save() to save the image to BMP file.
The resulting BMP file does not look normal. I think QImage::save() does not handle bytesPerLine correctly.
I have written a small program, that demonstrates this problem. You will have to create a sample 8-bit indexed image, that has width=6144.