Very small angles like that can be problematic. Besides the odd bit here and there like yours I've had the occasional wild join shooting off into the distance. The latter usually involved curved sections though as I recall.
As Jared says, try adjusting the reference lines.
The best way is to use: Design > Wall Extras as they allow you to change the settings while keeping the wall(s) in place.
Wall interactions can get quite tricky (like in the real world). Those links will help getting into some of the more subtle aspects of the art.
Cleaning up the reference lines didn't work in this case, but I have used columns to clean up the wall intersections.
Thank you Jared for the links... I knew I read it somewhere just needed someone to point out the obvious.