Communication diagrams layout troubles

[soril]

Hello,

I can easily make a communication diagram and it will look pretty nice. However, whenever I add another object instance near some other message arrows, the message arrows will usually move all around. That happens each time I add another element to the diagram and I have to click on each arrow to replace them back to their original location. It's time-consuming and unpractical !

Any way to fix it ?

Thanks,

Sébastien