clicking on the tick lines in click events demo does not work (clicks are
not picked up).

i managed to work around it by changing 

if(this.options.grid.clickable) {
	this.overlay.observe('click', this.onClick.bind(this));
}

to 

if(this.options.grid.clickable) {
	this.overlay.observe('click', this.onClick.bind(this));
	this.canvas.observe('click', this.onClick.bind(this));
}