Your observations match mine and others - on any current (and recent) Nikon DSLR, that's how the combination of Auto ISO and a Speedlight works.Personally, I always turn Auto ISO off when using flash, to avoid the ISO being ramped up unnecessarily.
BrianWelsh NikonianCheck out the Nikonians Team pages
Copyright © Nikonians 2000, 2013
All Rights Reserved
Nikonians®, NikoScope® and NikoniansAcademy™ are trademarks owned by Nikonians.org.
Nikon®, Nikonos® and Nikkor® are registered trademarks of Nikon Corporation.