You should probably have posted this in the 'How Do I' section.
Ashley's build post states:
"Auto-join room" is similar to "join room", but once a room is full it tries another room. For example auto-joining "myroom" with 2 max peers will put the first two joining players in to "myroom", the next two joining players in to "myroom2", the next two in to "myroom3", and so on. In other words, players get automatically assigned in to separate games with the correct number of players.
You can also optionally "lock" a room once it becomes full with this method.
Therefore. the lock option is part of the Auto-Join Action.
This implies there is no bug.