I've had a few screens do odd things, but I've not worked on an actual Ipad so I'm not sure, but I've fixed many phones/tablets/PC's etc, so I'm assuming this could be the same kind of problem ?
On some, it's literally just been dust/dirt/finger prints causing the touch sensor to get wrong readings (usually if a mark is hidden on the inside of the touch panel. Some cannot cope with even a tiny amount of grit/dust at the edges of the panel.
The odd thing to me is that some can take all kinds of abuse and still work perfectly, even with large scratches and marks on, as well as dirt and grease.
Note that some types of cleaning chemicals can also apparently have an effect on the special surface coating of some kinds of touch panel, but I cant say if that's happened to me or not, I do often clean screens using liquid Windowlene (not the cream version).
If a screen goes crazy at a certain point of fitting, i'd try (if possible) to lay in one end first, and then take it off and lay in the other end instead - just to see if it's the cable end causing the problem. But I would assume it's just down to the very very sensitive ribbons used that may break inside quite easily, I've had that happen on a few phones where it just didn't like being bent over even gently.