Why state change without myself knowing? ( short snippet )

pen: [ http://codepen.io/ustvarno/pen/grGJGZ ]
i have slider for changing speed of generations
so if u draw some squeres, and click to change speed before u click on button play, it will start playing.
This happens only if u actually click on slider bar, not on button on slider ( and drag it ).
What happens here?
Issue: line 174

This doesn’t happen for me. Chrome and Safari both behave normally. Maybe you were accidentally clicking on the button?

if u thinks button as button on slider, even if i click on that and slide left-right, why it would works?
On other hands i did not click play button after that, tried many times on google chrome and firefox…