WPA-PSK won't exchange keys using interface - wifi0

[Tony Espy]

i've run into a problem where i can't seem to get wpa_supplicant to 
complete it's key exchange with an AP using WPA-PSK over the wifi0 
interface.  it works just fine if i specify wlan0 as the interface.

we switched awhile back to using wifi0 for configuration of wifi ( ie. 
we start wpa_supplicant with '-iwifi0' ), and then use wlan0 as our main 
IP interface.  this allows our DHCP client (pump) to mark wlan0 UP or 
DOWN without interferring with the normal operation of the HostAP driver.

i'm guessing that this is a driver-level problem, but haven't been able 
to pinpoint the cause.

FYI, we're using a slightly modified version of wpa_supplicant 0.3.8 
with HostAP 0.3.9.  i've reproduced the problem with a non-modified copy 
of wpa_supplicant, including several older versions.

any help would be much appreciated.

thanks,
Tony Espy
Pepper Computer