Recent fragility with if_wi, 802.11 adhoc/wep, and Tiger

I fairly regularly use 802.11 adhoc with WEP to communicate between my 
6.x/7.x FreeBSD notebook using if_wi, and my Apple PowerBook running Mac 
OS X Tiger.  A few days ago, when I updated from a June to a July HEAD 
revision, this became quite "fragile".  Specifically, I often find that 
the Mac can't send to the FreeBSD box (ARP fails, etc), and that sometimes 
it will give an error when I ask it to re-connect to the ad hoc network. 
I find that if I ifconfig down/up if_wi, and likewise turn off and on the 
wireless on the PowerBook, it seems to recover.  I've not had a chance to 
really try and diagnose this at all -- i.e., does tcpdump show packets on 
either end, 802.11 state machine, etc.  I was wondering if anyone else has 
seen this problem, though.

Robert N M Watson