Rational
The invoice state showed from purchases and sales normally is very confused for many users because does not allow understand the really state invoice, for example in a sale with invoice state “Waiting”, is not clear if the invoice is in draft or valid, or post, there is a important difference between this states and the sales user need more explicit detail of invoice.
Proposal
The invoice state in sales o purchase must be same to the real invoice state,
If the invoice is “Posted”, the invoice state visible from sales must be “Posted” not “Waiting”