Vigorous Activity and Inaccurate Barometric and Elevation?

Hi, 

I have an instinct. When I do vigorous Activity, the Elevation and Barometric pressure readings will both elevate to a very high level for a period of a couple hours, then return back to normal. It's very strange and only seems to do it when I have an intense workout. Does anyone else have this issue? Is this issue related to the instinct or does the fenix do it too?