Yes, that would trigger it. Please can I see the code that you are matching with s _ , and for what purpose you are doing it?
Adventuron scans inside the on_command {} table for what looks like matching of directions, and adds in those directions to the exit list dynamically. The scanning is aware of additional inner if statements like:
: match "s _" { : if (is_at "stream") { : goto "moor"; } }
In the above case, it would add a SOUTH exit to the stream location.
What I'm really interested in is why you overrode the south command and why it's not appropriate to list the exit.