Purchase goals being triggered by a recurring subscription

OK - so this one has me scratching my head.
I have a campaign with a purchase goal in it.
There are existing clients who are on a recurring subscription for the product listed in the purchase goal.
Every time a subscription comes up for renewal the purchase goal is getting triggered - AS WELL as the tag that I have being set in billing automation after a successful payment.

I’m pretty sure this isn’t supposed to happen?
After all - the docs state
" buys through an manual order, order form, shopping cart or upon successful payment for orders created through the [API]" and as far as I am aware - a recurring auto payment is none of those?

Also - I look after a separate Infusionsoft server, and that one has the same components in place in one of the campaigns on there and the purchase goal only triggers on the initial purchase… after that the tag gets applied on every subsequent payment success as set out in the billing automation.

Am I missing something here? or is something weird going on?