1. Try asking in their support forum first. You're more likely to reach a developer or anyone who has ever used the program before.
2. Toast doesn't allow such things on DVDs (only CDs) and it's my understanding that it's because it's not part of the writable DVD standard. It may just be a bug that the program allowed you to do this with a DVD, in which case you might count yourself lucky the disk is even readable. I could be wrong about that, I haven't researched appendable or "open" discs in many years.