Hi,
Moving these events is not very user friendly at the moment. You'll have to drag the boundary event and wait until you see the orange layout lines appear.
In addition, in the 5.6 version the boundary events are best placed at the bottom of an element and then you can move them across the bottom part of that element.
I committed a fix to the trunk, which is also allows boundary events put at the top or side of an element.
Best regards,
