Texture Pack editing problem

When editing a texture pack and putting the edit in the texture pack it fails

What I expected to happen:
The edit would go into the folder, overwriting the previous file and work fine

What actually happened:
It would screw up and not work

How to do:
1. Make a texture
2. Put the texture in the pack
3. Open Minecraft
4. Try to put an edit in the pack

Demonstration: http://youtu.be/lLIWEFqEqkQ (not my computer)