It appears that the described issue is a bug for the RadCalendar control and I have logged it into our tracking system. Our development team will further research in this issue and will do the best to fix it as soon as possible.
As for the selected dates style, the required functionality is not supported with the disabled dates and you can not apply the selected style to them.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items