heres your problem
i may repeat it a few times so bare with me.
when you make an edit in the prv while playback is moving,by default the prv will stop scrolling.
its not a scroll key,nor a shortcut,,there isnt one.
all you need to do to get it scrolling again is right click in the prv timeline,anywhere will do(only in the prv timeline)
to reitirate:
try right clicking in the PRV quick zoom area.
in the timeline area...
when making edits in the prv when the prv is in motion(playback)
the prv will stop scrolling by default.
to restart the prv(start scrolling again):
simply right click in the timeline area of the PRV.
i prefer the quick zoom area because this way it doesnt bring the right click menu up and i dont have to get rid of the RC menu.
sorry if i havent read all the posts here,i just skimmed them.
but i think this may be what your talking about.