Events added in current month are incorrectly off by one month

The problem just started showing up on a site I have been working on. When I add an event with a starting date in the current month, the date gets changed somewhere between me pressing the post button, and the event getting saved to the database. In any case, the event shows up in the wrong month.

For example, If I post an event with a start date on April 23, 2015, the event will actually be posted with a start date of May 23, 2015.

Even stranger is the fact that this problem only effects events with a start date in the current month.
For example, if I post an event with a start date of March 14, 2015 the event is correctly posted. Likewise if I post a date with a start date of May 16, 2015 the event is correctly posted.

I have already checked to make sure the timezone is correct, and have combed the settings and found nothing.

Any help would be greatly appreciated as this problem has been plaguing us for the past few days.

https://www.ads-software.com/plugins/all-in-one-event-calendar/