Just a theory, but worth considering:
The club/Klopp realise they're only going to get the keeper they really want in the summer. Klopp also realises that in order for us to achieve anything this season, he needs Mignolet's form and confidence to improve in the next 3 or 4 months. So what does he do, he praises him, says he's happy with the keeper situation, and goes even further and offers a new deal. He's basically saying, "I believe in you". All the while hoping it pays off, Mignolet starts believing it, puts in a few decent performances in the run in, and we sell him to the highest bidder in the summer.
Could this whole thing just be a psychological confidence boosting tactic? Elaborate and expensive one if true.
No