Approval pending Reject functionality not working

Approval pending Reject functionality not working in below specific scenario:

Customization
Dental and vision plan force contingent on Medical plan with Exact tier match up.

if employee enrolled in to medical plan with Effective date 01/01/2017 to Null with EE tier
same employee enrolled in Dental plan with Effective date 01/01/2017 to Null with EE tier
as per contingency.

again employee increased tier EE+SP with effective date 08/08/2017 medical plan with dental plan went to approval pending

Pending Queue when we Reject Medical plan then contingent plan should be rejected also.

but above scenario contingent plan not rejected