Differences in iwspy !!!

Hi Folks,

  I have the same laptop running two different cards with two different 
drivers:

eth0:  Lucent Orinoco Gold               -> "orinoco-0.15rc3" driver
wlan0: Linksys WCF12 with pcmcia adapter -> linux-wlan-ng-0.2.2"

Both belong to the same ad-hoc group and are "iwspy"ing two other nodes 
which belong to the same ad-hoc group as well. A broadcast ping with 200ms 
interval ensures 'freshness' of the iwspy measurements. Here is what I 
see:

wlan0     Statistics collected:
     00:02:2D:64:5A:55 : Quality=32/92  Signal level=-100 dBm  Noise level=-132 dBm
     00:02:2D:64:5A:4B : Quality=36/92  Signal level=-96 dBm  Noise level=-132 dBm
     Link/Cell/AP      : Quality=0/92  Signal level=-100 dBm  Noise level=-100 dBm
     Typical/Reference : Quality:0  Signal level:0  Noise level:0

eth1      Statistics collected:
     00:02:2D:64:5A:55 : Quality=49/92  Signal level=-42 dBm  Noise level=-91 dBm
     00:02:2D:64:5A:4B : Quality=56/92  Signal level=-39 dBm  Noise level=-95 dBm
     Link/Cell/AP      : Quality:49/92  Signal level:-42 dBm  Noise level:-91 dBm
     Typical/Reference : Quality:36/92  Signal level:-62 dBm  Noise level:-98 dBm

Notice that the signal level and noise level are off by a very large 
margin in the two measurements.

Why is that ? The measurement cards are in two adjacent slots. I am seeing 
this very consistently.

I can provide more derails if anyone wanted so

Thanks in advance

Vikram