CME guarantees performance of contracts... Counter party risk of both sides of the trade. If MF Global blatantly steals your funds CME has no responsibility to make you a whole. If MF is counter party to your trade and defaults CME will back stop the trade.
Upon MF's bankruptcy active positions were transferred to other firms. Many positions were liquidated for lack of margin as client funds were locked up by the MF trustee. CME has an obligation to guarantee MF clients' performance of contracts as counter party to other traders. CME protected the other traders and unfortunately MF clients got margin called and liquidated.
The situation is a mess but the party responsible is MF global and their regulators. CME, to the best of my knowledge, back stopped the performance of all contracts.
No doubt MF clients got screwed but from CMEs' perspective moved the MF client positions to new firms who immediately margin called them in order to guarantee performance of the contracts to their counter party.