madwifi makes board crash after bursting packets

Hello madwifi-lists!
Hello hostapd-list!

Since I do not know, which of the madwifi-lists is still active and
read, I post my question to both madwifi-users and madwifi-dev.

See my setup below. If I burst data from one point to the other (lets
say with 'scp' a file of about 2GB size) at full speed (with the
distance I got right now (1m) about 23Mbit/s) the AP crashes after quite
some time (~1 hour). I am not able to check what is going on on the
machine that runs the AP, because the attached serial console won't
respond anymore and I cannot establish any connection to the AP anymore.
It is still transmitting beacons and can be recognized by any wireless
station (with the one being the client with 'iwlist ath0 scan' and with
a laptop not involved in the wireless connection on my desk with 'iwlist
wlan0 scan'). So I fear, I cannot give that much debug output, since I
can't access the AP anymore.

Rebooting the AP solves the problem immediately and the client connects
to the AP directly making data transfer possible again.

I could not reproduce this problem with low traffic, since I did a 'ping
-f IP' last night and it was still up this morning after 14 hours.

Running an iperf yesterday got the client crashed. Same problem - I
couldn't connect to it anymore via the serial console. Since it is not
transmitting beacons while being a station, I cannot tell, if the
wireless device was still up in any way.

My setup:

madwifi 0.9.4 - running on AP and Client
hostapd v0.6.9 on AP side with RSN-encryption
wpa_supplicant v0.6.9 on client side with RSN-encryption
2 PC Engines ALIX3D2-Boards (x86, 500MHz, headless systems)
Alfa networks MiniPCI-WAN cards with Atheros AR5414 chipset

I am using madwifi-0.9.4 on a productive system and I am not able to
switch to a newer driver within a recent kernel in a rush. Therefore I'd
like to stick with it, if that's possible.

Does this problem sound familiar to anyone? Are there any hints, what I
still might try before I am urged to move to a recent driver?

Thanks for any hint.

Kind regards,
Dennis