Rules reacting on an event that hasn't happened? Rules is acting weird all of a sudden. (v. 1.28)

It seems to be reacting on an Event that has not happened.

Using Commerce. Debug log shows that Rules reacts on the "Calculating the sell price of a product" event six times when I add a product to the cart, then reacts on "After adding a product to the cart", then reacts again on "Calculating the price", then reacts on "Select available payment methods for an order."

This last one seems really weird. We haven't even entered checkout. Why react on an event that definitely has not happened?

To make matters worse the Rules under the different events are firing multiple times, so I have customers receiving multiple emails and so on.

I have rebuilt the Rules cache. I have disabled Rules Conditional. I cannot understand why this is happening. Help, please?
Have a read of https://www.drupal.org/node/2403851 .

In short, Rules 2.8 is causing issues with Commerce. The module maintainers are aware and looking at the problem but until it is sorted they are suggesting rolling back to Rules 2.7.