Main calendar sensor logs multiple history events

[stormshaker]

I have a question about the behaviour I'm seeing. The main calendar entity (ie, the one named the same as the feed) has its state changed to On when there's an event, and Off when there's no event. This is helpful.

But, with a multi-day calendar event, there seems to be a new history event logged regularly - sometimes as often as every 5 minutes. The Off state is for exactly 1 minute. This is causing an issue with my Bayesian sensor that's observing it.

Just wondering if this is expected behaviour, maybe caused by HASS doing a feed refresh? Or is there something else going on?