Are you making the RFQ from a Material Request? What’s the UOM in the Material Request? It’s a reasonable request to expect the RFQ to use the Purchase UOM you have set, so unless you have done something wrong, maybe it’s a bug or an enhancement that is necessary.
I see your pain now. Looks like the way ERPNext is designed right now, if you want the Purchase UOM in the RFQ, you have to make a Purchase Request and that works as you’d expect it to work.