Thank you for contacting us.
We introduced our new RadDateTimePicker control this Q2 release and we made some required changes with date and time pickers. We tried to make as few changes to the controls as it is possible. Now RadDatePicker and RadTimePicker controls inherit RadDateTimePicker.
The answer to 1st and 3th question - I would suggest you to download our latest internal build and to use SelectedValue instead of SelectedDate. Try it and let me know if you still have any problems.
About 2nd question - I would suggest you to use ParseDateTimeValue event instead of SelectionChanged in your scenario. ParseDateTimeValue event fires every time when you type in the TextBox. You can use IsParsingSuccessful property of the ParseDateTimeEventArgs indicating whether the parsing is successful or not.
I hope this helps! I will be glad to assist you further.
the Telerik team
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