Script activates exponentially for some reason

1

is there any reason why the following code,

var KeyListener:Object = new Object();
KeyListener.onKeyDown = function():Void{
    if(Key.isDown(Key.TAB) && _currentframe == 1){
        gotoAndStop("pswd");
        trace("tab key pressed.  " + "Current frame = " + _currentframe);
    }
    else if(Key.isDown(Key.TAB) && _currentframe == 17){
        gotoAndStop("user");
        trace("tab key pressed.  " + "Current frame = " + _currentframe);
    }
}
Key.addListener(KeyListener);

would activate incrementally more and more every time the tab key is pressed? It activates once, then once again, then after that it activates the following number of times per key press event:
(number of presses - number of times script activates)
1 - 1
2 - 1
3 - 2
4 - 3
5 - 4
6 - 6
7 - 9
8 - 14…

Nearly locked up my computer the first time, when I kept mashing the tab key over and over again (must’ve hit it around 15 times).
:pleased: