Well unless the campaign manager specifically agreed to cover payments, or is otherwise holding funds to cover payments to participants, then there is no reason for campaign managers to pay participants out of their own pockets. They responsibility extends to managing the campaign and that is it.
I agree and don't think the managers should be the ones providing the funds.
However, I think they should get in contact with the runners behind and encourage them to step foreward and honor all outstanding payments.
After all I (for myself) think this is a task included in the responsibilities of a campaign manager.
(I edited my previous reply to make my position more clear)