Hi Brook
I’m hitting the same problem when testing with a clean install of WP 3.9.1, Twenty Fourteen, with only The Events Calendar and Events Calendar Pro (just purchased).
I’ve added 2 events in separate months with the intention of displaying any given month’s events in the sidebar using the mini calendar widget.
When the page loads, the widget looks fine: June’s one event is listed below the calendar. But when I click the arrows for next month (July), when it loads it’s the same June event. When I click on another month (to August), it lists the two June & July events!; when I click the back arrows, back to June, it then displays nothing. 🙁
Happy to let you have an admin to the installation if it will help you on the debugging.
Thank you for working on this as apart from this it’s a great plugin which the college is very keen to use.
Will