[SOLVED] TinyMCE strips gcse: google custom search from html even with portal_transforms disabled

When trying to use <gcse:searchresults-only defaulttorefinement="my-refinement"></gcse:searchresults-only> in html editing in Products.TinyMCE (Plone 4.x), even with disabled portal_transforms, instead of having this snippet rendered in a page view I get <searchresults-only defaulttorefinement="my-refinement"></searchresults-only>.

Does someone know if there's a configuration I'm missing or if this a Plone limitation?

Well, it's easier to just use their HTML5-valid div tags, so I don't need to mess up with all this portal_transform stuff.