Crashing when trying to make dialogue start at a certain part

I'm using version 5.0.9 on an iMac. I am trying to edit my game so that when my main character starts talking to another character the conversation begins on a specific dialogue part, rather than the 1st trunk of the dialogue tree. 

The editor is fine if I leave the action starting at the first level of the dialogue, but when I use the editor and select 'dialogue parts' as pointed out in the image, Visionaire crashes and I can't even view the dialogue branches to select one.

I've tried it on different characters but it crashed each time.

Has anyone had a similar problem or know what might be going on?

Thanks