That does sound highly unusual, they usually do a contract onboard a ship for months and change around when new ships get added to the fleet. There are all kinds of reasons for that change, may-be someone would know.
I was reading a december review on another site, and they said that in 2 weeks time, they changed captains 3 times on the Legend of the Seas. Is this usual? don't think so.
No, of course it´s not "usual". From what I heard, Captain Pedercini had to go home for family reasons and Captain Knutsen from SP substituted during a week, until ordinary reliever Captain Graucob returned after a shortened vacation.