Basically the Scheduler selection includes keyboard navigation which requires widget to be focused in order to work correctly. That why the widget listens on "focus" events and removes the selection when the widget is no longer the focused element. This behavior cannot be prevented out of of the box and custom solution would be needed.
For example you can attach custom "focusout" handler to the widget element and on each trigger to apply the selection manually (achieving this however would require using private methods of the widget).
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