Presently RadCalendar does not support Persian calendar style.

Currently, you can use reflection in order to access the properties of the fast navigation popup. 

Workaround: 
this.radCalendar1.HeaderNavigationMode = Telerik.WinControls.UI.HeaderNavigationMode.Popup;

CalendarNavigationElement a = this.radCalendar1.CalendarElement.CalendarNavigationElement;
FieldInfo fi = typeof(CalendarNavigationElement).GetField("dropDown", BindingFlags.NonPublic | BindingFlags.Instance);
RadDateTimePickerDropDown dropDown = (RadDateTimePickerDropDown)fi.GetValue(a);
dropDown.PopupOpening += new RadPopupOpeningEventHandler(dropDown_PopupOpening);

To reproduce:
- Add RadCalendar to a blank form and set its AllowMultipleSelect property to true.
- Select a date and deselect it right after that. You will notice that the background is not changed.
- The cell is actually deselected but it appears as selected since it is the focused cell and the styles are equal.

Workaround: Change the style for the focused state, which will allow the user to distinguish between focused and selected cells.

When you click on a Navigation Button with the mouse in RadCalendar and hold the button down, then it scrolls automatically to the next/previous views very fast. Same behavior should be supported by the Fast Navigation Buttons.

HeaderWidth and HeaderHeight properties should be made RadProperties and should be declared at RadCalendarElement. This will allow our users to set these properties in theme.

ADD. RadCalendar's TodayButton does not accept shortcuts.

Resolution: 
Add LabelFormat property to change the format of footer. You can use the following code snippet: 
this.radCalendar1.CalendarElement.CalendarStatusElement.LabelFormat = "yy/MM/dd dddd";

Currently the user cannot remove the FocusedDate of RadCalendar.

IMPROVE. RadCalendar - expose the RefreshVisuals method of the CalendarElement

Allow RadCalendar to have multiview based on years or months.

Resolution: With our latest release(Q2 2014) we are introducing new navigation mode that has very similar behavior the described one. To take the advantages of new mode you need only to set the HeaderNavigationMode property to "Zoom":
For example : this.radCalendar1.HeaderNavigationMode = HeaderNavigationMode.Zoom;

Adding the following method CalendardDayCollection.AddRange(IEnumerable Of Date) is an easy way to populate the collection

It will be nice if RadCalendar can show a popup list containing years. Currently, it supports only a list of months.

FIX. RadCalendar - add NewDate and OldDate to the SelectionEventArgs of the SelectionChanging event

Add functionality to apply custom format to the current date in the footer area.

Add functionality to customize navigation steps in multiple view of the RadCalendar.