I think the default timeout for WINS-entries is 6 days, so this could explain things. According to the RFC's the entry should be overwritten when an update is done, if non-secure WINS is running. If secure(???) WINS is implemented, a check is made to see if the old IP-address is still using the name. This is according to RFC; it could be that only a ping is sent to the IP-address...

Anyway, I attached the perl script...