This is SharePoint world and we see multiple strange behaviors of SharePoint sometimes. Today i have creating a new User Profile Service and created a User Profile Service AD Synchronization Connection. However, after populating the containers and creating a connection successfully i tried to add a filter in the connection but noticed that my connection is not editable. Whatttt???? Yeah... User Profile Service AD Synchronization Connection seems disabled and not showing the dropdown for edit. Here is how it looked to me.
I googled around but found no clue. However, a point suddenly hit my mind and i changed the Zone of my CA url from Trusted Zone to Intranet Zone in my IE settings.
Refreshed the page and Boooommmm.....! It worked.