Real Time Visitors no longer shows idle AJAX visitors. Problem with enableHeartBeatTimer?

Based on my nginx logs, it looks like there are about 30-50 people on my site. They’re idling because my site has background updates. Piwik tells me 0 people are on.

I’ve created an issue on this based on my findings with enableHeartBeatTimer not working reliably. It doesn’t seem to be running for every visitor.

But further than that - is there something else I should be doing to track those clients who are idle and requesting the background JSON update file?