I figured I'd jack one tire up off the ground to check for proper engagement and disengagement. Turns out both hubs are keeping the axles locked into the tires when I spin the tires (one at a time). I suppose all of those times that I had the hubs off must have changed something in them. They always whent back on fine and seemed to turn fine, so I never gave it a second thought.

Is there any other reason why the axle turns with the tire (some kind of friction absent of them being locked in?) other then the hubs need to be taken apart and looked at?