There is a bug in Telerik DatePicker in Windows 10 in certain locales.
UI always selects the current date, whatever date you type or pick.
Sometimes this current date is highlighted as invalid, sometimes not (capture attached).
This is most likely related to changes in date parsing:
I have tested with settings:
Culture ="Finnish (Finland)".
Windows 10 September 30 cumulative update didn't fix the issue.
I have reproduced the problem with the latest version of RadControls.