I’ve ran across a UFo that I’ve created with 10 Blue Zones and RoboFont Version 1.4 (built 1301142150) refuses to open them:
The document “Antithesis-Italic.ufo” could not be opened. The file isn’t in the correct format.
After I manually deleted a few zones, it opens fine. I’ve never heard that there can be too many zones, for sure not 10, so I consider this to be a bug.