That area that holds in the ball bearings needs pretty tight tolerances and every so often (mostly on AI's) a few people have problems. As long as there wasn't other reasons (damage) for that to happen, it would probably be covered under warranty. Be sure when you dissemble to replace the berrings you check for burrs, and probably sand both surfaces (Mast Collars) a little so it won't happen again.
See also: http://www.hobiecat.com/forums/viewtopic.php?f=75&t=33198&hilit=Ball+Bearinghttp://www.hobiecat.com/forums/viewtopic.php?f=75&t=12356&p=68770http://www.hobiecat.com/forums/viewtopic.php?f=44&t=8149
- - - - - Hobie Island Sailing since 2006 - - - - - 2011 & 2015? Hobie AIs and a 2012 TI