I am not sure of the combination that makes the scrolling pause, I think the most obvious is the Movie tag which will pause the scroll on that channel if the movie is listed, but I am sure there are others, for example I am pretty sure one of the channel attributes will make that channel always pause no matter what's on.
PG is a bit clever and if it had paused the scrolling while a another pausing programme was already on the screen (e.g. channel 24 caused the scroll to pause, and channel 25 wants to also cause a pause) it does not pause again until those channels have scrolled off-screen - hence the sometimes seen pause every 3 channels.
All of this does not rule out maybe another parameter somewhere that pauses for everything, but I haven't found it yet
