I've just talked to the developers about it. They will fix the issue in the next release.
What you can do now, to stay safe when the app renders your content correctly, is to place back the '+' and put your source block into an open block (open block: starting and ending by '--').
This works now AND will work after the next release.
Without the +, it will only work now and the level of numbering will break after the next release.