As others noted, the real issue involves the terms of the buyout. If the U is going to commit big $ to keep Fleck, they need at least some security that he is going to be around for a while - in terms of a significant buyout clause that would make it less attractive for him to leave - or make it harder for another school to foot the bill for the buyout.
Plenty of coaches sign extensions and leave within a year or two. It's just the nature of the business. Glen Mason famously said he would "answer the phone" if the right school called with an offer.
Unfortunately for Gopher Fans, I suspect you will continue to see Fleck's name tied to any major job opening - no matter what the terms of an extension might be. It's just something you'll have to live with.
It beats having a coach of an average program who is never mentioned as a candidate for other jobs.