Bug overview description.
As per RFC 4329 Javascript should be served with the MIME type application/javascript. Currently, it's served as application/json, which should only be used if it's plain JSON without JSONP wrapping, as per RFC 4627

This is important since browsers like Chrome refuse to execute Javascript if it's served with the wrong MIME type.
What part(s) of the site page(s) are affected?
All API pages with a callback query string.
What is the expected behavior?
That the document is served with application/javascript.
What actual behavior is given instead?
The document is served with application/json.
Can you reproduce the bug every time?
Yes.
What steps did you take to replicate this bug?
Visit any API page with a callback query string.

You might want to include the bit about it only affecting API calls with a callback query string in the title. As it is, it's easy to look at this title and think, "Well, let me check... Nope, application/json here, this luser doesn't know what they're talking about."

9 days with no response is a bit long for something legitimate like this, IMO.

Confirmed. Put into issue tracker. Should have a fix soon.

@Tynach: I usually process bug reports in batches when I have time to get to them.

Patch created, pending deployment.