Why rejected work confirmation display the category attachment "To Receiver" in which we can't attac

Dears,

Our case concerns the attachment at work confirmation level,

1. Create a new work confirmation, the only available attachment category is 'From Supplier' (grayed), the user forgot to attach the document and send for approval

2. The approver reject the WC

3. The user update the WC to add the attachment, now we have 2 Attachment categories ( From Supplier   and to Receiver), the user select 'to receiver' and attach the document,

He got the confirmation that the document is successfully attached but  the document in reality no attached to the WC

Would you assist on this ?   why displaying a category attachment that we can't attach to it ?