This is fixed on master.
It seems to be back again.
This might be one of those Schrodinbugs, but I got an
Unexpected end of JSON input while trying to upload an avatar.
This was after trying a few times, and getting rebuffed for having really big avatars. And finally, I found one which wasn't gigantic and it went up.
After that, I decided that I didn't like that avatar and swapped it for another one, and I got that strange error, but the avatar went through, from the looks of it
To clarify, this happened on these very forums.