Advanced search results: print view (from "print" icon) looks bad, has JS errors

Weird issue, might not be related, but I cannot get the print.css to enable itself when printing search results from the Advanced search.

• Go to Advanced search
• Click "search"
• on the results page, click the "print" icon of CiviCRM

Result: the search filter widgets take 90% of the screen.

Expected: no need for search filter widgets when printing.

At first I thought that the print.css maybe didn't hide those things, so I added a custom print.css on top of CiviCRM's default file (in an extension), but for some reason the CSS wasn't working. I don't see how a JS error would cause that to fail, but for some reason, none of the CSS is working. In any case, we should not have JS errors on that screen? (edit: see comment below, was because of media=print)