The behavior shown on the screenshots seems rather strange. Both controls should hide their popup element when it is blurred. For example when you open the calendar popup and click elsewhere on the page the popup should close. The same is valid for the dropdown of the RadComboBox control. Would you elaborate how are you showing the two popups in the same time?
With this said, note that in order for the calendar popup to be shown over the dropdown you should set the z-index for the calendar to be higher than the one of the dropdown.
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