Contours seem notoriously sensitive to toe settings. Getting them in spec helps, but the shop needs to go a step further. Have then get the toe close to 0 as possible, and have both the left and right toe settings resenble each other as close as possible (i.e., a little variation between each toe reading as possible).
Then again, it may be a rear control arm. I've bent one and it absolutely ate through the inside of my left rear tire (also front tire).
