This is standard behaviour in Tableau, and not just specific to v 9.3. The shape type you select is tied to the values (members) of the dimension across the workbook in the same way colours get associated. This is Tableau trying to help with data viz best practice and ensure consistency across the workbook. The reason you didn't get it when you first duplicated is because you changed the mark type. On your first map, the mark type of circle is automatic, whereas on the second you explicitly chose shape and then assigned a dimension to the shape. At the point you do this the members of the dimension become tied to the shape (the shape property of dimension member x is y). A dimension member can only have 1 shape property in the same workbook.
The workaround, is to duplicate the dimension (right click dimension -> duplicate), which will create a copy of the dimension, but is just another instance of it. Use that on your second map instead.
1 - I'm assuming this is what your first map looked like : Mark type = Automatic
2 - Your second map, duplicated from the first but with mark type = shape and dimension (in this case region) on the shape shelf
3 - Third map, duplicated from the second but using the duplictaed region (copy) dimension on the shape shelf instead
Hope that helps
Thank you for the reply. I realized I needed to simply duplicate the field that I was using and then it worked out perfectly
No worries - it would be appreciated if you could mark my reponse as correct, so the thread can be closed and it will help others searching with a simialr question.