I noticed that there was an issue opened up for IE8 for this issue on the google code page for dygraphs. It mentioned something about excanvas.js but from what I can tell in the current version of dygraphs excanvas.js has been removed.
The only time I see this issue is when I load the page on a mobile. I also noticed the title covers the top portion of the graph. I am not sure if the last one can be solved but I am hoping there is a solution for lines on the Y axis.