Minecraft Finger Rig Issue

I’m making a finger rig for a Minecraft character, but I’m having an issue with the drivers. I have sharp bends set up, but no matter what I try, one bend is not perfectly square. All three bends have the same setup but only one has the issue.



There is a small gap in the center of the (closed) finger. It’s driving me insane, and I’ve tried almost everything I can think of. Can someone please try to figure out what is causing the issue and tell me how to fix it? Thanks!

Download: Fingers.blend (493 KB)

Merry Christmas everyone (if you celebrate it)!

I modified the mid shape key.
www.pasteall.org/blend/25888

I also enabled some settings to make it easier to edit shape keys in edit mode.