My guess would be that it has to do with line weight. I may be totally out of the park on this one, but it resembles what one sees when zooming in to a CAD drawing with thick lineweights. They meet at the center of each segment, but their width makes them look like what I see in your bottom panel. Excuse if I don't use smilies, but it's my first response here.

I have been happily using Texture Tools for a few weeks, but seem to have borked them with the addition of other plugins. I have been backtracking to disable / remove some of the unexplored/less useful items, but wonder...are there any known plugin conflicts to avoid with TT V. 1.5? I reeeeely like it.