For https://github.com/HypothesisWorks/hypothesis-python this goes to Appveyor. Contrast Github's default behaviour in this case - it pops up a little box with the status and details of each provider, with individual links. Matching this behaviour would be really nice.
Sorry, which status icon and default behavior are you referring to? If you're talking about the one next to the repo title, it opens the popup for me as expected:

If you're talking about the one next to the repo title, it opens the popup for me as expected:

Not for me. The :x: links directly to the AppVeyor build. Maybe this only happens when one build failed?
Yep, that seems to be true. FWIW, we copy the icon from the first commit on https://github.com/HypothesisWorks/hypothesis-python/commits/master where it behaves the same.
Looks like a build misconfiguration or GitHub bug. GitHub's own icon in the commit list only mentions and links to one failed build. If GitHub doesn't have the popup in their code, we have no info to show.
(label is in HTML, but actually not visible to us)