I don't think voronoi was designed to support the refreshdata workflow.
voronoi is just a function which plots and returns handles. voronoi returns a handle h(1) to the original (x,y) data (plotted as markers) and another handle h(2) to the Voronoi edge lines which depend on (x,y):
x = gallery('uniformdata',[1 10],0);
y = gallery('uniformdata',[1 10],1);
h = voronoi(x,y)
h =
2×1 graphics array:
Line
Line
If you set the data source for the original (x,y) data, the Voronoi edge lines don't react to it when you call refreshdata:
h(1).XDataSource = 'x';
h(1).YDataSource = 'y';
x = 2*x;
y = 2*y;
refreshdata % the Voronoi edge lines will be out of sync
You're better off calling voronoi again on the new data to get a plot where the lines are in sync.