ECO changes all historical revisions of BOM with same changes as current revision

11.5.10.2 with no PLM.

New to Engineering and ECO's. When we update a parent item revision with ECO e.g C to D - I find that the component changes are not only being applied to D but also to C, B and A.So, e.g. if an item is used 3 per BOM and I change to 4 per for Revision D, all other revisions of BOM have an end date line with Quantity 3 and replaced with a new line for Quantity 4. If I then cut a job for Revision C (older ) I get the quantity of 4 rather then 3.

Is this standard functionality????. I would expect older revisions of BOM's to maintain the data and structure they were built to. So, in this case I would expect the Rev C of BOM wiuld have qty 3 per while Rev D would have qty 4 per.