Fuel gauge or sender question

Drove the 99 XK8 a couple of hundred miles today and toped up the tank after low-level light came on.
After filling yellow light was still on and gauge shows empty? After another one hundred miles gauge slowly goes up to full. Had replaced sending unit a couple of thousand miles ago and recently cleaned out a tank of old fuel and sender looked fine. Now have a full tank of fuel to consume before I can inspect. This seems odd to me a failure so soon?