Hmmm, that's the first I've heard of this but I can think of a couple of possibilities:
You may have installed an app on the phone that makes it think it's docked from time to time. If you've added any apps that have some special feature while the phone is docked, try removing them from the device to see if that clears things up.
There could be a problem with the hardware that physically connects the phone to the dock, which is tricking the phone into thinking it's docked even when it's not. If that's the case that's something to check with Samsung about since they'd be the ones repairing it.
If you do end up determining that you want to send your phone to Samsung, consider resetting it before you send it off to see if a reset clears the problem. Resetting your phone varies depending on what version of Android you're running, on Android 4.0 it's found under Settings > Backup & reset, for Android 2.3 it's found under Settings > Privacy. Note that resetting your phone will delete any data you had stored on it, such as photos or old text messages.