Graph does not show correctly when displaying a wide time range

[TheCookieMonster]

If I set my graph on any item to a short time range, the graph shows correctly:



However if I zoom out to a wider time range, it doesn't display correctly:
As you can see, when its zoomed out, you can see the green line, but it had this extra colour around it.

Does anyone know why this happens and how to fix it so that it just displays the clear line of the item data?

[TheCookieMonster]

The issue is even clearer on this graph:
You can see the green line accross the bottom, but then you also have the "fuzz" around it in a slightly transparent colour