I think I figured that Delaware poll out. Think about it. The Democrats wanted O’Donnell to win, so PPP released an honest poll on her. It worked for them. If they had wanted Castle to win, you would have never seen that poll.
Recall also that a few days before the primary, PPP had data on how Christine would fare against Coons. They deliberately withheld it till the day after the primary.
This is entirely consistent with your hunch that they wanted Christine as the primary winner.