I have a problem with our 'unlimited server' license.

I have the server license installed in our tree - right up the top (its a small tree) - the problem is when I restart a server it doesn't automatically acquire a server license. The license exists in the same level as the server object. The only work around I seem to be able to use is to use NWADMIN32 to manually allocate the license to a server - I know it shouldn't be working like this but it gets me running again - why doesn't the server simply acquire the license when it starts?
Netware 6.5sp5 - we only have 3 servers in the tree, all in the same container - same problem with them all!