Tested in 3.10 and could not reproduce the issue. When I set the 'Behind Desk Pickup Supported' setting to true, I was able to see the 'Hold is behind Circ Desk' checkbox in the patron registration and edit screens. I also confirmed hold slips stated the item should be routed to the 'Private Holds Shelf' if that option was checked. When updating the library setting values, I did have to log out and log back in to see the new value carry through.
Tested in 3.10 and could not reproduce the issue. When I set the 'Behind Desk Pickup Supported' setting to true, I was able to see the 'Hold is behind Circ Desk' checkbox in the patron registration and edit screens. I also confirmed hold slips stated the item should be routed to the 'Private Holds Shelf' if that option was checked. When updating the library setting values, I did have to log out and log back in to see the new value carry through.