I had a similar issue at an implementation in 2021, (Epicor BOM question - how does it know which rev to choose if multiple approved revs and how does View/Pull As Assembly impact this? - #8 by Ernie) and I got from support that when MRP creates a job, the subassemblies will ALWAYS pull their most recent revision (by Effective Date) regardless of the “Use Part Rev” setting (which only applies to top-level parts). In our testing, that turned out to be our experience as well. In that situation, the customer wanted to control the revision on the subassembly on a per-order basis, which would have required a significant customization (we specced it out but they didn’t go for it).
Your experience is counter to that… I recommend putting in a ticket.