OK, let's continue the story (in fact this thread is more and more like a developer diary ).
I am doing the map more complicated, by adding at the same time one region and one new owner faction. I started with only five regions for spain, gaul, carthage, greek cities (4 playable) and senate (non playable).
I have succeded in adding three more provinces for parthia, german and dacia, all the three playable, with no difficulty (only some silly mistake in coordinates or age of some child, reported with show_err).
However, when I tried to do the same with the julii, the game CTD with no error message.
It comes again the idea of the problem with senate missions when the map is not complete.
I'll report new findings.
Cheers.