Commenting and showing more lines not working when using custom domain. (BB-6190)

When trying to comment on a line of code or showing more lines of code, from a custom domain, the request fails due to being a request to a different domain.

XMLHttpRequest cannot load https://bitbucket.org/api/1.0/repositories/hora-de-la-papa/changesets/f3287d4d707a1e3827cf37d42a6a41158cb80827/_context/application/models/user.php?above_fnum=30&above_tnum=30. Origin http://g.20d.mx is not allowed by Access-Control-Allow-Origin.