It seems to mostly occur in the heading tags, but sometimes in the subsequent content.

It also happens in gmail, with specific emails from the same domains that have the issue on their site. I imagine this is due to the CSS being used and it has some character set that breaks the browser.

Here is an example

Well, I tried to add an image, but I get an error
"×ERROR
Something went wrong while parsing server response" (it's only 228kb)

But it changes the text from normal English to something like the following:
"Sxoder ne C' s' Hm rs' shrshbr"

When you Copy/Paste the text, it is normal, though.