I've never seen this mentioned before anywhere and it seems like a bug a to me.
When a ship on autoexplore reaches the very edge of the map, it goes off autoexplore and becomes focused. Pressing W again doesn't help. I have to tell it to go to another unexplored area and tell it to autoexplore again once it's there. I think getting to the very edge of the map confuses it or something. I've seen it in 1.0 and 1.1.