Multiple event entries after a single eventTrack call

I’m making a single call:
_paq.push(['trackEvent', 'doc', 'Clicked TOC CTA', 'xxxxx']);

I see that a single request has been made to the endpoint. However when I check analytics for this event, I see that from a single call, the event counter has increased not +1, but +4(sometimes +6). I’ve checked the DB, and I can see multiple new entries from a single call.
How do I interpret this? I’m expecting just a single entry.

Piwik version: 2.16.1

At the top in blue - new entries in the DB,
at the bottom, a single trackEvent call: