When kiosk mode is activated all four window borders can be accessed and used to resize the kiosk window with a mouse or trackpad. This gives the user access to the underlying windows which then deactivates the kiosk mode and makes the OS fully accessible. This behaviour was introduced in FileMaker 14. Also the kiosk mode isn't really full-screen as it was in version 13 as there is a small gray area displayed at the bottom where the scroll bar used to be, on Mac OS 10.11 this is also the case with the scroll bar on the right. On Windows everything seems to be fine though.