When you have given your currently selected unit an order, the game automatically selects the next "suitable" unit that have available moves.
Sometimes this helps, sometimes it just messes things up. It would be very helpful to have an option to disable this behavior. Also a menu item and a shortcut to toggle it.
If you can define specific circumstances that "mess up", we can disable autoselection in those cases. There is (was?) a longstanding open bug in this area.
I've noticed a similar behavior. In Europe, when you Train an employee, the focus on a specific unit changes to another unit, and again if you Train another employee.
Fixed in git.6929269.
Notice, Caleb made a specific complaint, and it got fixed (eventually).
Woohoo!