to the left: 1bit-alpha channel
to the left: 8bit-alpha channel
Scroll down and then slowly scroll back
up. The above PNG image using 8bit alpha-transparency should not
be upside-down.
You can see that the 1bit-transparent PNG is not affected.
Now you're prepared to watch another even more scary effect...
turn on the alternative stylesheet 'fixed background'
(via View->Use Stylesheet->'fixed background') and scroll again.
Would perhaps be a nice effect, if it was intended this way.
Well, what I see and expect you to see also, is: the 8-bit alpha PNG scrolls
up to the top of the page, seeming to stay there while scrolling further
up (to improve visualisation, I've added red borders around the images for
this stylesheet). Gotta see this yourself. =)