monitor mode in Belkin Components F5D7050 Wireless G Adapter v4000

Hello,

I have a:
Belkin Components F5D7050 Wireless G Adapter v4000

$ dmesg | egrep "zd1211b? chip"
[30382.403185] zd1211rw 1-4.4:1.0: zd1211b chip 050d:705c v4810 high 00-1c-df AL2230_RF pa0 g--NS

if I turn the device in monitor mode there is no signal strength value in the radiotap header.
i have tested this with wireshark and libpcap.

$ uname -a
Linux infrared 2.6.39-02063903-generic #201107091121 SMP Sat Jul 9 11:25:36 UTC 2011 x86_64 GNU/Linux

$ iw dev wlan2 station dump
Station 00:XX:XX:XX:XX:XX (on wlan2)
	inactive time:	21350 ms
	rx bytes:	7703
	rx packets:	268
	tx bytes:	7420
	tx packets:	106
	signal:  	39 dBm
	tx bitrate:	1.0 MBit/s

so the signal should be in [-127 to 0] ?!?
what is iw doing if there is no rssi value given? network manager shows some tiny signal.....

on my other device (ralink based) everything is fine.

thanks, christian