Something you've changed in your page code is forcing page reloads every X seconds, which has the completely undesired effect of causing the 'Back' Button in your browser to be less than useful.

If you've been watching a 5 minute long video, you may have had the page reloaded that many times, so click back to return to where you were only to have to do it 4 more times as EVERY one of those refreshes is inserted into the browsing history.

It's sloppy and a really rather annoying way to, I assume, get more page impressions for your ads?