Array.prototype problems

i wrote an array.prototype function which added an unique element, but then all the comboboxes behaved strange. i tracked the problem down to this

Array.prototype.doesntmatter = function(element) {
for (var i in element) {
trace(i + ' ' + element );
}
this.push('wuzaa'); // this adds extra lines on combobox component. doesn't work with this[this.length] either
}
list1.addItem("?!");

, and add a combobox named list1. somehow, this function is called whenever i click on the combo, (which add extra items) and afterwards every time i hit a key. outputs things like this

target _level0.depthChild0
type reveal

target _level0.list1
type keyDown
code 17
ascii 0
shiftKey false
ctrlKey true

does somebody know how to fix this, other than creating a function with the array and new element as parameters?
flash mx 2004, v7.2