In the past, when I have updated a property that is connected to a form, it automatically updated the drop-down on the form for me. In the new form builder, the expected behavior is that you need to manually go into the form and choose to include the newly added option on the property for it to appear. I understand why this was done, but I think a better alternative would be to choose if you would like to changes on a property to be automatically reflected or not. Having to go into every single form a property is used every time a change is made is illogical.
I would envision this as a pop-up after hitting save when you make a change on a property. You would check mark from a list of forms that the property appears on if you would like the update to be reflected.