No, V5 and previous had no problem running 6V on any servo.
I suspect that perhaps they changed it due to the back emf on high current servos damaging the BEC.
Even so regardless they still recommend a buffer pack as nothing is 100%.
Jazz BEC IS useless unless you run a little 450 or 250.
There is NO problem with the jive BEC, just be aware V5 or earlier you can run 6V, V6/7 you need to set to 5.6V (stock) unless you have BLS servos then you can run 6V.
There is plenty of info on this including a response from kontonik go to there website or use the search