Scroller with ease small fix needed

I have a good fla file for scrolling with ease. It is working fine but with small issue.

Find attached fla and swf file.
When we run it first time it is perfect.
First you click ‘down arrow buton’ and scroll it. After this, again when you click ‘up arrow button’ at its last , the content movie clip keeps moving 1 or 2 pixel up and down contineously. Which is not needed. it should be static at its top position.

Can anyone help me? its 2 minute job for expert person.

Thanks in advance.