PNG End Bytes Significance?

[Omniscient]

It's the streaming endbit which means on a streaming download like an internet connection the file might not load properly.

When you're downloading any file there has to be a method to know it's completely. Unsure what is inside the PNG header bits but it may not provide enough info for a file to know it's ended.

Try your edited PNGs on a remote host and see what happens in a browser.