[Observium] Negative values in the ICMP graphics

Hello,

I'm running Observium 0.13.6.4115 updated today and I see negative values in the ICMP graphics, it also fails to draw the preview images. I update Observium weekly from svn.

http://i.imgur.com/xGCoaHJ.png http://i.imgur.com/3Hmtj2A.png

The same Draw error is visible in the ICMP Statistics, ICMP Informational Statistics, IP Statistics and UDP Statistics graphics.

Any clue to get it fix it is welcome, thanks in advance.

Cheers