BUG in date format handling using d/m-Y format

In WordPress I use the following date format: d/m-Y showing for instance 15/04-2014
When I edit an appointment (logged in to WordPress) the UI displays the date correctly, but when I save the appointment, then the list of appointments shows it wrong. The month and day fields are switched! When I then choose a day above 12 the date fails completely and 01/01-1970 00:00 is used!
Using the frontend, visiting the page where a client is requesting an appointment, then the date format also fails the same way.

This is fatal for me
I just bought the plugin, just installed it and testing it.
Please help