iPhone 3GS Personal Hotspot showing 2 connections

After connecting to Bluetooth Network with my MacBookPro Personal Hotspot initially shows one connection then after a moment it shows 2 connections. connections. Once I disconnect the laptop it reduces the count back to 1 connection.

I first noticed it after update to latest iOS 4.3.3 but may have happened after 4.3.2. I know it worked fine in 4.3.1.

This is happening at home where I'm confident there shouldn't be any other devices.

It persists in both wifi and 3g including after wifi is turned off on iPhone and wireless router unplugged.

Does anyone know where the mystery connection comes from?