I've caught this bug for many times. I've create a diagram via StarUML & save it. From time-to-time my diagram needs some updates. So, I open *mdj-file, make some changes & save it. And so on, and so on...
After some days or weeks, StarUML open file... and there is nothing in interface: nothing in working diagrams & nothing in model explorer. And that means that all my work is ruined.
I've attached the problem-file called "Classes.mdj" to this message