Ok your right, this is def. a bug when accessing the storage processors through Unisphere client.  Our other hot spares (we have 1 per DAE) have user specified LUNS.  If we do automatic it wants to make this new one LUN 6, and I thought you should start your LUN id's at 17 and go up from there.  Anyway I was able to bind and specify LUN id 206 using Navisphere Manager by using my laptop and Firefox to go directly to the IP of the storage processor, rather than entering the SP's IP through Unisphere Client.
Getting this error: The user capacity entered is invalid.  Please enter an integer between 1 and 9223372036854775807.
How do you create lun for hot spare (NX4 with AX4-5F8 backend)