Why would a Mitral valve leak only a few weeks after an Aortic valve replacement?

[Luce3701]

Our son just had to undergo another OH Aortic Valve replacement in just 3 months after the first one.  He was born with an Aortic defect which his Cardiologist has been watching for over 20 years.  He had his first OH surgery in May and the second one, using a tissue valve, in August.  The Mitral valve developed a leak and he had to be taken by ambulance to the ER just a few weeks after the first surgery with Congestive Heart Failure. They drained the fluid and he was released from the hospital, but ended up going back several times after that.  He was put on Lasix for the fluid.  Finally , the beginning of August, they did a test and saw that the Mitral Valve was leaking.  A different surgeon totally replaced the Aortic valve and the root and did repair work on the Mitral Valve.  He is doing much better now, but the second surgery was much harder on his body.  Is this a normal scenario using a mechanical valve?