Please refer to line 1165 of events-calendar-pro/events-calendar-pro.php the enqueue_styles() method, and in line 2129 of the-events-calendar/lib/the-events-calendar.class.php the loadStyle() method.
Both use the is_active_widget() function. And in wp-includes/widgets.php line 1140 the function is declared and used internally by wp_get_sidebars_widgets() as described here: http://codex.wordpress.org/Function_Reference/wp_get_sidebars_widgets .
This function retrieves the list of sidebars and its widgets, this means that is you use the_widget() it won’t work.
We already resolved this issue. We just wanted to let you know this could pose a problem in the future for your plugin and the_widget() function.