Hi Jim
The Separation action functionality is make the employment status Withdrawn.
Hence when you run the separation action the status is getting changed to Withdrawn.
This you can see in the personnel action configuration in PA side, there is employment status that will be set to 0.
If your requirement is to keep the employee active with the default position then you have to configure another action type which will keep the default position but change the employment status to active in that action type.
hope this helps
Thanks