css gets added on ajax load even though already in page

In my use case I'm using the local fonts submodule of fontyourface on a views list, that gets added to by an infinite ajax pager.

I found that even though the css for the local fonts was in the page, it was getting repeatedly added with every ajax render. For some reason it can't tell that the css is already present.

The effects of this were most pronounced in Firefox, with all font face text briefly disappearing and reappearing with every ajax load, presumably because it re-renders the text (on the whole page). Mostly just created performance problems for the other browsers.

I coudn't figure out why the ajax_render() core function was unaware of the css already added by this module, so I just added a hook_css_alter which removed all css in ajax responses, which doesn't really seem like a good solution.