I just used the Black Ink Beta to draw my first picture with it. It got pretty well, but then I tried to save it again for one last time. Then it happened.
Black Ink crashed and stopped working, the problem is that I have a corrupt save file of that picture now. I guess the programm deletes the save file and replaces it by a new one right away, instead of creating a temporary file and overwriting the current one after the creation is complete.
I hope this problem gets fixed in a future update.
I always back up the current file now before attempting to save.