Bob - Id be surprised if it is meant to do that, as you have proved it is very dangerous in the wrong situation.
My new 60hp Mariner has what Barrus call an 'engine guardian system' basically this means the ECU monitors the engine and when something goes wrong it minimises the risk, ie: Engine oil gets low, the EGS backs the revs off to 2000, the cooling system is faulty - same effect, 2000 revs, and over revving, possibly caused by the prop out of the water - the EGS cuts it back to 2000.
Could have just been one of those things, but may be worth having it checked out...second thoughts, after last time - maybe not!!!