Offset path sometimes extends in both directions

I've noticed an issue that happens very rarely, that is when I use offset path, the path will extend the desired amount in both directions. Below is a photo that illustrates what is happening. On the left is a shape I pulled from a PDF that I'm working with. The right side is a rectangle of similar size. Both shapes have had a .5" offset path applied. On the left you can see that there is a path that's basically 1", half and inch in either direction, while the right shape performs as expected. Anyone know why this happens?