It's a known issue: when you cross a sim border on a vehicle, your avatar is often unseated. Meanwhile the vehicle sails on into oblivion without releasing your controls.
Every time it happens I'm going to post here until it's fixed. Feel free to do the same.
Date, Time, Location
Sept 9, 5:20pm, flying from Oak Grove to Morris
Sept 9, 5:24pm, flying from Rizal to Morris
Sept 9, 6:02pm, flying from Oak Grove to Morris (noticing a pattern here)
Sept 9, 8:02pm, flying from Minna to Varney
Sept 9, 8:09pm, flying from Perry to Lusk
Sept 9, 8:12pm, flying from Morris to Oak Grove