See ticket 1444254 for details.
The start and end date for the widget is set during the component load and will trigger another function. It's impossible to change and capture the date range change from that point on without more coding - messy.
The behavior should be,
The implementation seems unfinished and unusable (at least for my use case)...it is really worthless as it stands for a date range utility....might as well just implement 2 calendar inputs and code for selection - I did this in another framework and it kinda sucked to do :-). This widget's expected behavior, its potential would be a big time saver for a dev if it was coded more in the spirit of its name.