Is this a bug or a feature?

[Luke <..hidden..>]

In 1.2.18 (yeah, I know...):

One can not change the income/expense account on an inventory item, if 
that item is already associated with, I suppose, an invoice.

If the item has not been sold (I assume that's the criteria), these 
accounts can be changed freely.

The question: is this the intended behavior?

If so: what is the financial reasoning?

Regards,

Luke