They might be saved incorrectly. Check if the point coordinates from the XML file form a straight line. E.g. create a straight Bezier arrow starting from 0, 0, save it with your code, open the resulting XML file, and verify whether the x/y ratio of all point is the same.

In addition, make sure the point coordinates aren't converted to integer values when saving or parsed as integers when loading. That might add some offset, depending on the MeasureUnit that you use.

Stoyan