We've noticed that setting both the essid and the key helps a lot with the automatic detection various procedures, such as end-user laptops don't get automatically attached to essid's that happen to be advertised without keys by other end-users' laptops.
I expect you'll get a bounch of nodes in adhoc mode with the ietf5X ssid and the ietf5x wep key as well...
If my node has mode "managed" it will never attach to laptop nodes having same key same essid but mode ad-hoc.
(my linux node, I know not about windows drivers).
Alex