Well, this might be an NG/MAX thing, but I have my doubts about that.
Here Mentour Pilot, a 737-NG pilot, talked about how he had exactly this problem.
Watch from Minute 12:00
https://www.youtube.com/watch?v=aTS4BEKqi4U
Also I watched a flightdeck video where this exact thing happened on an NG. Unfortunately I can´t find it anymore, despite my best efforts to hunt it down. They flipped the lever up, gear stayed down, they closed the flap properly and the gear came up.