Phase One is quite little company compared to giants like Canon or Nikon, do not overestimate their production & test budget

We all know how buggy digital (not Phase One only, to be honest) backs, especially old ones. For P and P+ series, for example, voltage is very critical factor - even 0.1V deviation can lead to unstable behavior. New batteries designed for current generation of digibacks, electronics also made step forward.
Of course, if unexpected reboots is not a big problem - just forget it. I hate it.