In case it helps anyone I will post what worked for me.
I had to plug my S3 into a direct USB port of my PC for it to prompt me to accept the RSA signature. I had my S3 plugged into a hub before then.
Now the S3 is detected when using both the direct USB port of the PC and via the hub.
NOTE - You may need to also run adb devices
from the command line to get your S3 to re-request permission.
D:\apps\android-sdk-windows\platform-tools>adb devices
List of devices attached
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
9283759342847566 unauthorized
...accept signature on phone...
D:\apps\android-sdk-windows\platform-tools>adb devices
List of devices attached
9283759342847566 device