Whenever I use a forming tool in a sheet metal assembly, the forming tool contains a ? in the feature tree.

When I check the references, every thing is OK and I don't have any broken or out of context references.

The images bellow show the feature tree and the references window.

Now my questions:

1. What does this ? means?
2. How can I prevent it to appear again?

an assembly and the forming tool is attached if you need to test it.

Thanks for any kind of advice.