Iain said in email the situation is;

""Our engine runs fine and has given us many many hours of happy service and we maintain that a happy engine means a happy boat. The problem occurs when we go from in gear to neutral. More often than not the engine will simply stall. It starts as quick as a flash when turned over but as you can appreciate this is all rather concerning when entering marinas (although we’ve only spent 6 days in them in 2 years!). The rev’s at tickover are still the same as ever and we service the engine religiously every 100 hours. The fuel pipes are only 2 years old and the fuel is always treated and clean.

We’ve been living with the problem ever since it started in the Canaries in Sept 2012, but we do think it is gradually getting worse.

The engine is a fresh water cooled Volvo Penta 2003.""

My first thought was the throttle linkage or fuel IP shut off switch is getting opened when they throttle down and shift into neutral. Anyone have any good ideas I can pass along?(he's not interested in throwing it overboard )