Just write another test
http://jsfiddle.net/gv7spbLc/The expected result is moving line without trailing.
If the result is incorrect, change the flag closePath to 'always' or getContext2d to 'always' to see if the issue is solved or not.
Thanks for looking into it. This test also works fine for me, but still no luck with the charts. Wish I could be more helpful than that!