Dimension mirrored from reality

I have been working on a part for a few days now and have come across a strange thing. Several features in the model are defined using a sketch on one of the standard (front, side, top) planes which is then extrude cut from an offset to that plane to an offset to that plane. In other words, a sketch on the front plane is being offset a distance away from the front plane, then extruded towards the front plane by a distance that is determined by a lesser offset from that plane. The pros and cons of this method can be debated seperately but the result of this is a correctly modeled feature with a dimension that is mirrored. I have attached an image below to better show what I am talking about. Is this a bug or is it a direct result of the method I am using?

The first picture shows the settings and sketch I used to set up the feature, the second shows the resulting mirrored dimension (0.519 dim)