Katafter a lot of bemusement, frantic debugging, and Automatticians questioning our collective grasp of reality, we discovered that one of the default fonts (Merriweather Sans), which was being loaded from Google Fonts, had published an update with some bad ligatures (special characters in a font that even out the space when common letters are joined together, like f and i).
this font was used in one of the default themes so it affected a LOT of sites. but the post editor used different fonts, which is why it didn't show up while editing, only after publishing a post.
since the font wasn't versioned and we were serving it through Google's CDN, this update had silently propagated to any site that was using this theme, without us needing to deploy anything (meaning not only was this hard to track down since we hadn't made any changes, we also couldn't easily revert the change). voila: Fs were going missing on tens of thousands of blogs (as well as other places around the web)
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