User blog comment:Rappy 4187/Technical Update: May 20, 2015/@comment-3388044-20150521160714/@comment-452-20150521194831

For future compatibility, it might be best to change the H1 to a H2, since that is how Wikia are fixing the problem.

Or, make sure you explicitly set every CSS property you want to use for the H1 in your side bar, with !important, so that future changes will not effect it.