The following caveats exist for line groups, route groups, route/hunt lists, and route patterns/hunt pilots:
*No voice-mail profile exists for a hunt pilot number. Immediate Divert and Call Forwarding to voice mail are not allowed.
*No forwarding is allowed for a hunt pilot number.
*Call pickup is not allowed for a hunt pilot number
I thik the issue must be related to this bug CSCsa66224. Upgrade the CallManager to the latest patch