good points but i would like to argue that if kushina ever truly did lose control then it would be dealt with at an earlier stage in the transformation, as in long before the bijuu completely emerges. minato with sealing techniques would most likely be the first method.
Originally Posted by Majere
it's also good not to forget that kushina could have, for any intentional reason, gone into any stage of tailed beast mode and allowed kyubi to use its power (beast bomb). it's likely minato would be close. what is almost certain is that any beast bomb minato would have witnessed from the kyubi would not be in the context or scenario of an attack on konaha or else it would have been something mentioned already. maybe minato and kushina fought side by side and used the kyubi's power a bit. they could have even been battling another beast or jinchuuriki.
Yea, if Jiraya and Orochimaru could change, redo the seal, then Sandaime and Yondaime could've done so as well (Minato even did it once for Naruto)
Kushina having special chakra to contain the Kyuubii doesn't actually mean she never lost control, just that it wouldn't happen as easily as with another host.
And I don't think that the host losing control is always intended by the village. First of all, most jinchuuriki have weaker seals than Naruto (because only the Uzumaki clan and Minato knew the stromgest seals) with Bee maybe having the second strongest. The "hole" in the seal only allowed merge Naruto and Kyuubiis Chakra over time, because Minato knew that he would need it.
Maybe it's even the reason Naruto could transform at will at the beginning of the time skip, but it doesn't have anything to do with the Kyuubii itself taking over Naruto now and then. It has been established that the Bijuu can overtake their host more easily when they are filled with hatred (therefore Naruto always automatically transformed when he got really angry, whether he wanted or not), so it's not too far fetched to believe Kushina was overtaken by anger at least once.
Besides, the people of Konoha (Jiraya, Yondaime, Yamato etc) seemed to know too much about Kyuubii and how to seal and stop it in the first place. How should Jiraya have known to stop Naruto's transformations if neither Kushina, nore Shodaime's wife (who had the same chakra as Kushina) lost control? The last person to actually see the Kyuubii, or a jinchuuriki transformation of it, would have been long dead by the current generation. (I guess shodaime hokage)
I believe that every host must have lost control of his Bijuu every once in a while, maybe with the exception of Rikuudo Sennin.