It's no surprise that banks have been scrambling like mad to get a piece of Blackstone's $13.5bn debt financing for its acquisition of Thomson Reuters — it's the biggest buyout package since the financial crisis. Yet one feature of the contest is raising eyebrows.

To get on the deal — and get a slice of the fat fees available — banks have had to jump through all the usual hoops. But even battle-hardened financiers have been surprised to be asked that their banks pledge to maintain spending on Thomson Reuters' data services.