The Cayman Preferreds are under dispute according to the MOR so I would say it's uncertain as to what is WMI's responsibility in the payout.
Seems to me it's one of those open items like the tax refunds.
Here's the SEC 8-K filing. The language to me implies it would be a WMB asset ... not sure why WMI would need to cover it's value. There must be a reason why Rosen mentioned it, though.