I have the same problem. Just a short trick, to come around that:
1. Close StarUML
2. in Finder, right-click on the file and use open-with
3. Search for StarUML as the relevant program (select "all programs", to be able to select StarUML)
4. StarUML opens and gives you the diagrams... :-)
I am not sure, everything comes over correctly (my collegues work on version 1 Windows, while I only have a Mac at hand). But at least I am a bit further.
Hope that helps anyone, until the "normal" way to do this gets fixed (and maybe also a clue for the developers, where to look)
Cheers
Jochen