No... that's not the way a compass is supposed to work. What you're describing is the behavior of a device that does not have a built-in magnetic compass, and therefore can only derive heading information from movement. Your $250 Garmin is designed to be used while driving, so therefore doesn't need a magnetic compass. The
hiking Garmins in that price range generally do include a compass.
The whole POINT of including a magnetic compass in these devices is so they can sense heading without movement. That goes for phones, gps's, anything.
That being said, while I've only had the Epic for like 10 days, my compass seems to work pretty well. It's accurate to magnetic north. East and west show some variation (15 degrees maybe) and south is close. I wouldn't want to use it for long-distance backcountry navigation (hell, who wants to use ANY compass for that in the days of GPS
) but it's sure good enough to make Sky Maps and the like usable. Sometimes it takes a few seconds to "wake up" when an app that uses it is opened, but once it orients itself it does all right.
Joe