Change BOM using Change Documents - different rules for same material type

Dear,

We have two materials (material 1 and material 2) code for same product type and we would like to change it using the transaction code CS02 and:

For material 1: The system shows us the message that it is mandatory to inform a change document number to change it;

For material 2: The system does not show the message and we get to change it without the change document number.

We´ve checked and both have same status from BOM,

For material 1 we dont have any change documents created earlier;

The change documents has been not used when the material 1 was created;

For material 2 curiosly we have one change documents assigned

The change documents has been not used when the material 2 was created;

I am confess you we dont know what is missing and I was wondering if you could help us to identify this error?

Best Regards,

Valdevair