Why are my SVG paths distorted?

Hello,

I've saved down a bunch of icons from Illustrator as SVG to be made into an icon font.

Most are just fine.

But a few of them are distorted, the points and curves are jumbled by just a little bit here and there ... apparent when I open the SVG file back in Illustrator too.

In the example below, you can see that the edges of some of the shapes have moved when saved down (the font is Helvetica).

Is there a step I should take to save shapes down correctly as SVG from Illustrator CC 2014?

Regards,

Pete