Event Manager calendar Month Picker shows wrong month

I use the Event Manager plugin to show events on the site. When you look at the calendar, it shows the right events of the current month. But the month name in de month picker shows the name of the last month.
For example: the current month is april. The name in the month-picker is march and the events in the calendar are the events of april.

Which files or settings ca I change to solve this problemen?
The version of the plugin is up to date.