I was going to ask why my upload never finished, but this was more interesting:
This is an actual HTTP header returned by the URL
https://s.yimg.com/pw/combo/1/3.11.0 during the "publishing" phase when uploading images. Could it be related to privacy- or ad-related add-ons breaking the uploader?
I am a pro user, and I have never had any infractions or other guff in my account history.