Emoncms Multigraph fill below curve

Hello
A while ago, I noticed a minor issue with my outside temperature Multigraph (otherwise great by the way - well done). The "fill the area below the curve" feature doesn't seem to fill anything less than zero on the vertical axis. The vertical axis auto scales; the line displays a negative value but no fill below zero. Am I doing something wrong?

29/12/2014 - UPDATE

Ok. Cold again last night and now I see there is negative fill from horizontal zero axis to the negative line.  Looks good now.  Thanks.