I dont think there's any problem with the gap that you see. When moving the panel around with the mouse that's the same spot that it "springs" back to. I am using a "fade" effect though so I'm glad that it works that way. No complaints.
As for the suggestion, I'd like to change the UIScrollView script and not my own, so that I do not need a "fixer" script for every scroll view I have. It definitely seems like something that UIScrollView should be responsible for anyway.
Also, there's actually a second "bad offset" issue going on that might/might not be related. I am quite sure that this is either an NGUI bug or an NGUI "gotchya" that I'm not aware of. I've included a screenshot of it in this reply. The area that I tinted blue is a UIWidget, and the area tinted purple contains UILabels.
As a bit of background, the text only falls out of alignment when doing a position tween on the top-level parent of the whole "window". As you can see, some text is scooted too far to the left and clearly falls outside of its own bounding box which should never happen. Its completely random in which labels get effected, and if you scroll the content off-screen it will sometimes correct itself.