Re: dojo head bans students from training with another teacher (ex student)
It does appear to be unfair for a dojo leader to prohibit other from attending your dojo. A couple questions came to my mind.
You state that the person starting the new dojo left "for good reason" does that mean you have a great deal of confidence in him or her, or that the "old" dojo has it's problems?
Also, are you happy with your training & your instructor?
I think that whatever happens, you need to consider weather you are happy with your experience in the old dojo, and if not if there is any way that could be changed.
Even if you are free to go to the new dojo, you will still need to consider which dojo you want to be affiliated with. There is also the consideration of weather the hours in the other dojo will "count."
It will probably be up to one of the heads to determine your progress and when you are ready to test. Which person do you have the most confidence in to guide your training and progress?
In my opinion, you probably will need to choose weather or not you are forced to choose. It would make sense to me to go to practice with the person who is guiding your training.
Whoever it is you decide to go with, bear in mind that not attending the new dojo head's classes does not doom this person to failure. Go only if this is the person you really want to stay with long term.
If there is some danger that your move could cause long-term bad feelings from the "old" instructor, that might be something you may want to consider. It's doubtful his actual feelings will change even if a decision is made to allow people to go. Things may be difficult to impossible if you ever want to come back.