Keep in mind that it is not the failure or shorting out of electronics that keep people from rolling down their automatic windows after entry into the water. It is simply the pressure the water exerts onto the window surface. (Even if it is only a fraction of a pound per square inch, the window has many square inches!) This external pressure could effectively prevent you from manually cranking the window down as well. I believe this was shown on the MythBusters car dunking episode, but I cannot remember for sure. Either way, better to be safe than sorry.