7.1.X, 7.2.X, 7.3.X, Master
1. Set up DXP 7.1 with the latest fix pack and start it.
2. Go to Build (Site Builder on master) --> Pages and add a public page as a widget page type, and on Page Configuration go to "Advanced" and go to "CUSTOMIZATION SETTINGS" and enable it, then enable Customizable for both "Column-1" & "Column-2"
3. Go to the Page and from the upper right click on "+" and add an Alert Portlet (or any other portlet that can be added only once"
4. Refresh the Page
Checkpoint: Issue: if you go to the application menu and check the Alert Portlet, you can add another one.
Result: you can add the alert Portlet again.
Expected Result: The once added Portlet type may not be added again.