Our servers are using AMXX 1.8.0. Ever since the Steam update we havent been able to use amx_ban or amx_addban with any success. It says they are banned, it kicks them from the server but they are able to rejoin immediately.
This is the case for banning for a certain time period and permbans. The permbans arent being written to the banned.cfg as well.
Oddly though, amx_voteban does work but that isnt very practical to use because of the short ban length.
Maybe the fact that voteban works and ban doesnt might give someone a clue as to where its failing.