Nothing wrong with this!
If you change the match a bit, the S11 graph (on Smith chart) may encircle the center of the graph, and then you will see negative phase also.
If you would add a quarter wave transmission line between the actual feedpoint and the source, the S11 curve will be in the negative half of the Smith Chart. You may know that adding a 90 degrees long transmission line (50 Ohms, assuming 50 Ohms reference impedance), will rotate the curve on the Smith chart over -180 degrees.