On an A319 flight from IAD to PDX last week, the lone lav in the tiny F cabin was indeed open, in fact it was available to any passenger in any cabin who wished to use it. Consequently, queues were fairly long at times.

However, about an hour before landing, two FAs gathered in the galley and unlatched at least two of the catering carts, which were then deployed to block access to the galley/lav area. No special announcements or admonitions were made.

A moment later, the two pilots emerged from the cockpit successively and, I presume, took care of their business. Once this task had been successfully completed and the pilots back in the safe confines of the cockpit, the catering carts were returned to their proper places and the FAs re-disbursed to other sections of the plane.