Hi Dinko, I cannot provide you with my solution, however I am providing a couple of screen shots to see if that will help illustrate the issue. Note that in the first screen shot, date-1.jpg, I am just "textually" changing the date, not using the 9 square icon to select a date, or choosing the selection if it pops up. date-2.jpg illustrated how the date pops up if you textually change it.
If I click Save in my UI, it will not Save the date, and goes back to the previous one entered. Is this the way the RadDateTimePicker works, or is something wrong. Some of our users have complained that they don't want to select a date or use the 9 box, they just want to enter the date and click save.