Herton Ronaldo Krzesinski [off-list ref] writes:

quoted

I also wonder how Herton encountered the problem :-). Older
wireless-testing simply say "unimplemented" or something if one
tries to set power-saving. Maybe Herton has a few devices which he
routinely tries out every part of iwconfig?

The original sequence of commands:
[1] /sbin/ip link set dev wlan0 down
[2] /sbin/ip link set dev wlan0 up
[3] /sbin/iwconfig wlan0 power on
[4] /sbin/iwconfig wlan0 essid any
[5] /sbin/iwconfig wlan0 power on
[6] /sbin/iwconfig wlan0 essid <my AP>
[7] /sbin/iwconfig wlan0 key open <my key>

That show the issue on rtl8187b I have to test just is near on what Mandriva 
2008.0 ifup-wireless script does, so that's what first made me catch the bug. 
the '... power on' after '... essid any' is what causes later the association 
or any scan attempt to fail, if I place a sleep between [4] and [5] I don't 
get the problem too.

Thanks for the clarification, this kind of information is important
when reporting a bug.

The problem is, I couldn't see yet how a power on after essid any
could cause this.

I'm guessing that it has something to do ieee80211_ioctl_siwpower()
calling ieee80211_hw_config(local) which ends up as an extra call to
rtl8187_config(). I do not know why this is a problem for rtl8187b.

It would help if you, or someone else seeing the same problem, could
provide more information by enabling MAC80211_VERBOSE_DEBUG and
MAC80211_LOWTX_FRAME_DUMP config options, and sending the kernel log
output here. I don't have a rtl8187b card myself so I cannot test
this.

-- 
Kalle Valo