Thanks for your feedback. 
1. I will change the condition to combined grammars only, my mistake. 
2. I guess you are right that the relaxation of the condition might be too relaxed. I assumed the use cases you described are covered by existing tests (and they all passed). I have only written a test for the use case were the defined tokens in `tokenVocab` are referenced in the parser (as a side notice, should I open an issue for this bug?)