This issue can be reproduced in your own demo application at http://demos.telerik.com/silverlight/#ScheduleView/FirstLook
See the attached screen shot for instructions on how to reproduce. When you have followed the steps in the screen shot, save the appointment. Then open the same appointment again and open the recurrence pattern. You will notice that value in the "day of month" box has not been saved. It now displays 0 instead of the number entered in the previous step.
I will also tell you why this is happening: You have removed the property DayOfMonth (which was obsolete in the Q1 version) without updating the xaml template accordingly. The "day of month" box is still trying to bind to the DayOfMonth property (nullable int) when it should be binding against the DaysOfMonth collection ( int ). Please make sure that this is fixed in an internal build soon.