Hello Karim,
As an experiment, I wanted to see if the issue affected OM 6.2, since I could reproduce it on both OM 7.3 and OM#, I did get a little further on OM 6.2, but it did eventually crash as well in exactly the same fashion. I seem to the issue most frequently when connecting boxes or adding new boxes. OM 6.2 mentioned a crash log, so I had a look, and it does seem to be some sort of GTK thing. I can atttach the log if you think it would be useful.