Ok, so I seemed to have found a reproducible case for the collider duplication issue.
Steps:
1. Create a Sprite Collection.
2. Add texture (I use point filter, 2D Physics, and have 1x and 2x sprites for settings).
2a. Create polygon collider and commit.
3. Create a new tk2d sprite using the new sprite.
4. Rename and add a 2D Rigidbody and create a prefab from the object.
------Up to here everything is fine------
5. Create new texture in Photoshop and overwrite the texture and @2x version in the asset folder (with Unity open).
6. Open the Sprite Collection and click commit, the collider will be duped at this point for all sprites in this collection that are in the scene.
Normally I would edit the collider in step 6 but I found that is not necessary to reproduce this behavior.
I assume this behavior is not expected.
For now I will try to avoid editing textures once they are in the project.
Please let me know if the steps I take are not "standard" or if I should be doing something else.
Thanks,
Jacob