I just updated to 4.8.1. I found that on one of my sites a portion of the page suddenly looked very strange afterward, with extra space above a particular site area.

This was a text widget with just a shortcode in it, nothing else.

It was tricky to track down - unlike most such appearance quirks/errors, it wasn't CSS this time. I tracked it down to paragraph opening and closing tags with no content.

After fiddling some more, I replicated the problem in the same way I did in my other comment above. (to reiterate) If I stick HTML code or a shortcode into a text widget, make sure there are no extra spaces, and save it in Text mode, all is well. If I go back in, change nothing, make sure there are no extra spaces, and happen to save it in Visual mode, this magic annoying extra bit of empty paragraph code appears, and things look funny.

It sort of seems like wpautop gone awry. :)

I'm thinking that if someone has their CSS set to add no padding or margins for paragraphs, this may slide by unnoticed on their site, even if the errant P tags are there.

The good news - the Custom HTML widget seems to be working.