Wrong z-order for Sequence Diagram's Self Message text (#106)

Hi,

I a sequence diagram, if I drag a Self Message onto a Lifeline which doesn't have an Activation Bar yet, the Bar will be automatically created.

Unfortunately, the Message text will be painted below the Bar, and parts of the text will be obscured if it is long.

The text is painted correctly (above the Bar) if I create the Activation Bar before creating the Self Message.