Link problem

My problem can be found at

http://www.skolresurs.fi/matteva/geometri/linjer.html

The m-symbol in the left down corner is a link back to the start page.

It works fine if you use it in the first frame, that is before you click Start.

If you click the m-symbol later on (after clicking Start) it does take you back to the start page, but the browser shows a lot of the code in the address!

In this case I have the following code in the the button’s actionscript :

on (release) {
	getURL("http://www.skolresurs.fi/matteva/index.html", "_top", "GET");
}

I have tried moving the link to first frame:

MlogoBTN.onRelease = function() {
	getURL("http://www.skolresurs.fi/matteva/index.html", "_top", "GET");
};

But that made it even worse, then even the first frame gave the garabage in the address field. At least some of the time…

Why does this happen and how can I prevent it? I am definitely interested in the why-part of my question!