Map by default when the server is empty?

[jamz]

...So this should always be the first map/mode combination that a person will see upon entering the server.

This isn't quite true. The maprot keeps going when the server empties. This means if there are two or more entries which accomodate for 0 or 1 player/s, the next one in the list will load on the next player join. In your example of the default maprot.cfg, if all players left the ac_scaffold game, the next maprot entry to apply would be this one:

[SELECT ALL] Code:

ac_desert     : 2: 8: 1: 0: 4: 1     // dm, 8 minutes, 0..4 players

If you want only one map to be the 'join' map, make sure it's the only maprot entry for 0 or 1 player/s.