IDE :: SWF Slows Down When Key Get Pressed And Hold

My actual project I need a event configuration wherein I can hold a keyboard key down and move mouse. While trying to implement this, I recognized that the flashplayer begins to lag, saving actions in buffer and playback them when the KEY_DOWN event is already over...

For example I have a
PHP Code:
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler, false, 0, true);

And in the handler I got only this:
PHP Code:
private function keyDownHandler(event:KeyboardEvent):void {
if (event.keyCode == 88) manoverDrive = true;
} 

I also do have a
PHP Code:
stage.addEventListener(Event.ENTER_FRAME, enterFrameHandler);

In this enterFrame I do animation for a movieclip that is animated regarding the mouse and keyboard action and events. Now when I hold down any kind of key the animation of this moviclip gets slown down if I hold down the key for 10 seconds and then lift the keyboard key the mouse movements I made before gets somehow saved and the animation got a playback of the mouse movements. I removed the keyboard eventlistener and the behaviour stays. Is that an official flash player Bug?