Water wisteria also just kinda does that. Apparently it happens to a lot of people...who just pick off the deteriorated stem bit and replant with no apparent harm to the plant. 1 of my 3 wisteria did the same..it's a bit shorter than the other 2 but still growing like a weed (I've woken up to brand new 4 leaf clusters that opened and practically doubled in size by the time I got home from school.) Also, If you decide to get more wisteria, It has a bit of an acclimation period for a few weeks before the crazy growth period.