How about this possibility? Maybe D. Vernon Parker was on the defense mitigation witness list, but refused to appear for his interview with Juan on the ground that he had already spoken to the defense and told them he had nothing to say in favor of Jodi and wanted off the list ASAP, and the defense agreed to take him off the list. Then Juan said, well hey, maybe I need to talk to you after all because it sounds like you might have something helpful to say on my side, and VP said, I would really prefer not to be involved. [Now somewhere in all this there must be a subpoena or threat of a subpoena, or I don't get where the judge gets the power to "order" him to participate.]
And then the defense said, but wait, your honor, remember when we had the sealed hearing about whether we could argue XYZ at the mitigation trial, and you called VP on the phone to preview what kind of testimony that would involve, and then you said no, we can't argue XYZ? That topic is off the table, right? And the judge said right.
Disclaimer: This is just a guess. I know nothing more than any of you.