Appropiate Ban Methods

[I'm a zambi]

Leaving the server to avoid a ban does nothing; I'm sure he's aware of this.
You can type '/admin', goto 'players' and select 'ban disconnect player' and he'll appear there if he's disconnected.

Where is this demo you mentioned? You said you had it but you haven't uploaded it.
Edit (Demo): Attachment 8809

I just finished watching the demo and all throughout I was wonder what you were talking about as far as an exploit. As far as I'm aware, using the ladder that drops from its originally unclimbable position is fine, since it's set to drop at a certain point in time (for example, with 2 minutes left in the round). I think the issue was more a lack of defending a newly opened entrance than an exploit. His leaving the server was probably because he didn't want to play the next map, seeing as the map ended and he didn't simply disconnect (unless he disconnected on the next map?); regardless, I don't think he was trying to avoid a ban, nor do I think he 'exploited' anything on that map.