You're right, I'm able to make out the effect on my desktop screen when dragging windows from side to side. I guess we only scroll vertically most of the time,

You're right, I'm able to make out the effect on my desktop screen when dragging windows from side to side. I guess we only scroll vertically most of the time, not horizontally, so it doesn't come up. That suddenly is no longer true when you rotate to portrait orientation.