bridging trouble - far nodes not bridged

[Scott Serr]

[I'm sorry if this seems like the wrong list to post to, but I bet you
guys do this implementation successfully all the time]

I have 2 USR2450 wifi routers that are hacked and run LinuxAP.  (these
were earlier and wimpier equivalents of the WRT54G running an embedded
386sx and prism2)  LinuxAP is kind of old: 2.4.20, hostap-0.0.4,
bridge-utils-0.9.6... all crammed in a 4MB firmware.

My problem is:
Close neighbors can see eachother, but far neighbors can't.
No routing here, just bridging. 

In a 192.168.x.x/24 network:
sparky (.4.1) -- usrAP (.4.243) -- usrSTA (.4.222) -- pc(.4.10)
                                 ^
                            wireless link

sparky = UltraSparc/Linux with a Realtek 8190too
usrAP  = USR2450/Linux/hostap, wlan0 and eth0 in a bridge (br0 =
192.168.4.243)
usrSTA = USR2450/Linux with wlan0 and eth0 in a bridge (br0 = 192.168.4.222)
pc     = XP with a Netgear FA310 NIC

The AP and STA are communicating fine, the wireless layer doesn't seem
to be the problem. 
Sparky can ping usrAP and usrSTA, but not pc. 
pc can ping usrSTA, but not usrAP or sparky. 
usrSTA can ping EVERYBODY. 
usrAP can ping everyone but pc.

usrAP and usrSTA bridges both have stp on, hw ether macs set the same on
eth0 and wlan0 before bound in br0. 

I think my problem is with usrSTA, since when "sitting there" I can get
everywhere.

Has anyone seen anything like this?  I've got about 8 hours in this
problem now, if I find the answer -- I'll post it.

Thanks,
Scott