Talked to support and got it fixed.

Navigated to <username>/Library/Preferences, and removed com.omnigroup.OmniGraffle.plist

Then opened Console, searched for omni, and cleared the display.

Then re-ran the terminal command, created a new line, and everything works as expected!

Visio Export Issue
 

I just switched to the new line behavior. For the most part, I love it. One thing I don't love, though, is that it now seems that exporting to Visio does not make the new arrows appear correctly. With the new behavior, when an arrow is connected to an object (pointing towards it), the end point lies in the center of the object while the arrowhead actually appears at the border. Perfect. But when the diagram is exported to Visio, the arrowhead extends all the way to the center of the object, where the endpoint lies.

One of the main reasons I purchased the Pro version was for the Visio export functionality, as I use it heavily for my work. Unfortunately, this little bug is making my diagrams that contain arrows look pretty awful after they've been exported to Visio. Is there a fix for this? Thanks!