The documentation for BoM variants states that you can add multiple variants per BoM line, presumably to include that BoM line in an MO created for any variant listed on that line. In testing when more than one variant was specified on a given line that line did not appear in an MO generated for any variant.

For example, say we offer a two-piece vehicle seat (base and back) that's either tan or black and heated or unheated. The base is heated or unheated but the back has no heater option, just a color choice. In the "all variants" BoM I created a line for each of the four seat base combinations, each with one variant selected. Then I added the two seat backs, each with two variants selected, one heated and one unheated.  In this configuration no seat back winds up on an MO created for any of the four variants.

To get it to add the seat back to an MO I had to add the same seat back product to the BoM twice more and add heated variant to one, unheated variant to the other -- not ideal. Is it failing to work like the documentation suggests or is there something I'm not understanding about how it should be functioning?

This BoM fails to add the seat back:

This BoM adds the seat back but isn't the desired method:

Using Odoo 11 Enterprise, verified it functions this way in a stock runbot instance.