I'm having some trouble using the lip & groove tool. When I create the feature, it changes the geometry of the solid it was created from. The picture below illustrates the problem. Along the right side, everything is fine, and the new body created matches the slope of the part (2 degree draft angle). On the left side, however, the angle has changed, and now the surfaces of the two solids do not align.

I tried selecting various planes for the direction of the feature. The best result I can get is a plane perpendicular to the right surface.

Below is another example of the good angle/side:

Below is the example of the bad angle/side. You can see along the top that the surfaces of the two solids are no longer contingent, which they were as a single part before I created the feature.

I'm not sure how to resolve this issue. I'm open to doing some secondary adjustments after the feature has been created, but so far I haven't come across anything that works well. I do currently have a gap between the lip and groove, of just 0.1mm. Adjusting this does not seem to make a difference, nor does change the angle of the lip/groove. Please let me know if there's anything I an do to clarify the issue. I attached the part file as well.

I'm currently using Solidworks 2015 x64.