AirPort network sometimes forgotten?

I have a PowerBook G4 and an AirPort Extreme base station. I typically
range around my house, accessing the network from a variety of
locations, though typically only from one or two.

Here's the strange thing -- every now and then, when I open up the
laptop and wake it up, it is no longer set to be on my AirPort network.
In other words, on the AirPort menu, no network (there's only one) is
checked. I have to reselect my network, re-enter my keychain password,
and then all is well. I'm back on the network. But that's a pain!
Most of the time, I just open it up and go. Why does the laptop
sometimes forget what AirPort network it's supposed to be on?

(Note: I haven't noticed that this problem is a particular problem from
a particular location, and it is definitely not related to phone
interference. I have never yet had trouble with the signal strength
not being adequate, and I'd think it highly unusual if the only time
the signal dropped out just happened to coincide with me waking my
laptop.)

Any ideas?

--
-Thomas

<http://www.bitjuggler.com/>