CiviEvent registration does not clear additional participants if later removed

As written by a client:

I originally chose to register 2 people, me and Vicky2. I filled in my info, then filled in Vicky2’s info, and just before the continue button where it says “Your registration will not be submitted until you click the Continue button. Please click the button one time only. If you need to change any details, click the Go Back button below to return to the previous screen.” I decided not to bring Vicky2. So I clicked “back” all the way to where it asks to choose how many people, changed than to 1, clicked “continue” and then on the confirmation page Vicky2 was still there - no way to get rid of her! So the issue seems to be that once you’ve selected a number of registrants you can go up, but you can’t go down.

I tested this on the demo site, and it works as she says. It appears that CiviCRM doesn't clear the fields if you pare down the number of participants.