[Window] Window is initially unresponsive when dragging starts

[dtopalov]

There is a small, but noticeable delay between the user interaction with the Window and the actual start of the dragging.

Observable (in the online demos too) only on the initial mousedown over the Window, and if the dragging movement starts immediately after the mouse button/trackpad is pressed. Once the dragging starts, dragging works as expected from then on until the mouse button is released.

Upon starting the dragging anew, the issue is again observable.

Further details in this public support thread:

https://www.telerik.com/forums/kendo-window-performance