Hi Sankar Kumar,
After an additional review from the development team, we've confirmed that this behavior is not a regression - the DateRangePicker is intended to bahave like so. By design, the calendar popup should close after a valid selection is made. Selecting a new start date that is before the current end date effectively results in a valid date range selection, so the popup closes.
That said, I have marked the item with a "Won't fix" status as it is not a valid bug/regression. In a future product version, we may consider providing an option to keep the popup open in this scenario. This will be tracked as part of the following item: Review DateRangePicker selection UX.
Regards,
Nadezhda Tacheva
Progress Telerik
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