Nested products with serialnumbers for sub-products

I have a problem with nested S / N.

I have an end product (A) which contains a BOM with 3 other products (purchased parts, B-C-D) with activated serial number function, each of which has a manufacturer serial number.
Then I created an MO for the product (A) and reordered missing parts.
When receiving the purchased parts (B-C-D), I have to enter the manufacturer S/N or something similar.
When processing the MO, I can assign a serial number for my end product (A) and also have to enter an S/N for the purchased parts (B-C-D).
This S/N for the purchased parts (B-C-D) can be freely selected instead of only being able to select the S/N assigned at goods receipt and not yet “used” S/N via pull-down menu.

Is this a bug, unexpected functionality, not yet implemented functionality or is my approach wrong?
The Dolibarr version is V14.0.2 on Windows10

Thanks in advance