This is normal behaviour.
Unless you really take youre time and the tank is empty when refueling, yes then it will get leaner.
After refueling pressure will be higher, and the engine will be fed more. same reason why you experience leaning out at the end of a tank.
when full it will be richer, when allmoust emty - it will be leaner.
How to cope: tuning when tank is half full, and dont fill the tank to the rim, nor run it dry.