I'm not sure how they obtained the status of ex-partners, but there is a relatively new feature that I think you can probably use to fix them. 
	- 
		Click on one of the step parents
- 
		Click on "change or delete" on the left
- 
		Click on "Change partners"
	From there you can make any changes pertaining to whether someone is a current partner, an ex-partner, or an extra partner.