The only way to fix it is to go into the XML code and remove (rewrite) the code that is sending key commands each time through the control loop. Many developers do not test to verify a key command needs to be sent, before sending a key command to FSX in the gauges. It is more expedient to just send the command without a test since it has no undesirable effects on single player mode. This causes the command to be propagated to the MP server multiple times a second. If the code that send the multiple key commands is in a gau file or in the model, you cannot do anything except ask the developer to correct the code as it is not modifiable by anyone but him.
Dave