Add Performance Goal button is Enabled When No Goal Plan is Assigned in ESS

The page is associated to the employee's inactive work relationship, and there are not defined review period (as expected).
However, as you can see in the screenshot below, the + Add button is enabled. 

When clicking on this + Add button, the user to redirected to the new goal page where goal information can be entered.
No goal plan can be selected. This is expected behavior as no goal plan has been assigned to this assignment. When clicking on Add to submit goal, the following error appears: