Could have had a wheel well fire warning - requires gear down for 20' to let it cool. (Although they'd probably land back for that). How about a gear down transit flight to the maintenance base - perhaps with damaged gear doors / retract mechanism?
Surely, if putting the gear up causes the aircraft to stop climbing while the gear is being retracted, this is illegal? JAR /FAR regulation stipulate a minimum ROC after T/O for obstacles etc. If you can't make that, you are too heavy to airborne. The only time you are allowed to fly level is to accelerate during flap retract. Interesting rumour though.