Keep in mind that for all clients in AirWave with Aruba, there's 2 different ways we parse for device type. The 'AOS Device Type' is grabbed from the controller directly, while 'Device Type' is calculated based on the client device thumbprint. When the field changes, what are examples of the change? If it's from OS X to AppleTV, that is possible depending on data the controller got initially. If it's a more apparent change like say from iPad to Win7, then that's something that screams support case to gather more information to debug.