I think it’s a problem with the maturity of the madwifi driver. But there is good news. Atheros have released new linux drivers for there most recent wifi cards
http://madwifi.org/wiki/news/20080725/ath9k-atheros-unveils-free-linux-driver-for
The ath9k driver includes supports for the following chipsets:
AR5418+AR5133
AR5416+AR5133
AR5416+AR2133
AR9160
AR9280
AR9281
Hope these will be incorporated in Zeroshell