Why doesn’t the Back-Annotate Assignments command in the Quartus® Prime Software save the pin locations?

Description

Due to a problem in the Quartus® Prime Software version 18.1, the Back-Annotate Assignments command doesn’t save the pin locations after a successful compilation and generates the following message:

The Quartus® Prime Settings File changed outside of the Quartus® Prime software and contains errors. Rewriting the Quartus® Prime Settings with current state of assignments in the Quartus® Prime Software.

Resolution

To work around this problem, you can manually enter the pin location assignments in the Pin Planner, the Assignment Editor, or the Quartus® Prime Settings (.qsf) file. 

This problem is fixed beginning with version 18.1.1 of the Quartus® Prime Pro Edition software version.