Legends in graphs seem to upset the W3C validator

The validator seems to be happy with the SVGs as far as the legends, and then finds that elements appear where they shouldn't. The first error occurs on a g element with a class of "legend":

<g y="25" x="415" class="legend">

"Attribute y not allowed on element g at this point."

Not sure if this is a validator bug, or if this is a bug in our graphing library, or a bug in Atlas.