This is because disqus treated the two URLs as different and therefore loaded different streams. If you want the http and https URLs to have the same comment streams, you need to specify the canonical url in config disqus. Here is how I did it:
<div id="disqus_thread"></div>
<script>
var disqus_config = function () {
this.page.url = "http://www.oddprints.com/help";
};
(function() {
var d = document, s = d.createElement('script');
s.src = '//oddprints.disqus.com/embed.js';
s.setAttribute('data-timestamp', +new Date());
(d.head || d.body).appendChild(s);
})();
</script>
<noscript>Please enable JavaScript to view the <a href="https://disqus.com/?ref_noscript" rel="nofollow">comments powered by Disqus.</a></noscript>
, config http url url, page.identifier. , , , http, disqus.