I'm trying to apply a Lip&Groove assembly feature to my part, but after the feature is created, the outside surface of my part has changed. It appears it's changing my draft angle on the exterior. I made sure that the "Maintaining Existing Wall Surfaces" box is checked.

Before Feature is added.

After feature added. The top-half exterior surface angle has changed, and no longer coincides with the bottom part. There's now a new lip that has been formed, and the exterior surface on the top part angles in rather than out in a proper draft angle.

I've played around with the settings for a while, but haven't been able to figure out why this is happening. If I'm overlooking something, or there's more critical info I need to mention, please let me know. I'm using Solidworks 2015 on a Windows 8.1 machine.