its seems to be a fontTools issue
it seems to recalculate the bounds from all points instead of analysing the bounds of the contour
(this will be fixed in the next version...
I re-looked at your topic after a tweet https://twitter.com/arialcrime/status/537553252783759360
And if I remembered it correctly it wasn't an issue when I tested on 10.7 but now I see the issue
This will be resolved in the next update
Well I was to quick pushing a new version of the Outliner. The developers and beta version of RoboFont has a warning for a typo in the API. Which is solved in the Outliner, but you don't have the dev or beta version
thanks and good luck!