Let’s walk this through.
I am a candidate and I find out while I have low poll ratings that a Super PAC that said they supported me started dumping large sums of its money to an actual competitor. It is illegal for me to talk with anyone there, but I can go on national television and complain that it appears people who claim to support me are shifting their money to my competitor. Doesn’t that make me look like even my supporters are doubting my candidacy in favor of another person with similarly low poll numbers?
Some things are best left unsaid. Cruz, to his credit, negotiated around that huge loss of support and became the only viable competitor to Trump.
It appears by not telling the world how weak he was to his supposed supporters helped him in the long run.
They have Ted Cruz's picture on the site. They proclaim they are supporting Cruz. They solicit money on the basis of supporting Cruz.
If they are collecting donations for purpose A, and spend that money on a competitor, then they are engaging in fraud. Cruz would have a duty to not be a party to that fraud, by telling the world that this PAC should no longer be considered to be on his side.