Why does editing one button make changes to another button as well?

If a button was created from a template(by doing Copy Button and then Use Same Button or by selecting Add Button From Library) two buttons can be linked together so that changes to one button affect a second button. To unlink them;

1. Right click one of the buttons and select Remove Button From Page from the popup menu.
2. Click on Yes if it asks if you want to remove the button from the page.
3. Now right click on the same button that was just removed and select Create New Button from the popup menu.
4. Now you should be able to edit this button without it affecting any other button.