I notice that I'm able to book and fly BRS-FRA-NRT-MUC-BRS (for examples sake) on one ticket. Another good idea.. I assume there is some sort of agreement with Lufthansa already in place?
I'm not sure if it's by accident or by design. The fare engines may be holding onto the fact that the BRS-FRA route had a BD codeshare when operated by LH, so the BRS-BM/LH-FRA component may actually have been an autoconvert from BRS-BD/LH-FRA. The fares were never deleted when LH pulled the route, and a whole bunch of them can be used still as BRS-SN/LH-BRU- routings. It only seems to apply for fares to destinations EAST of Europe - you can't use it to book BRS-FRA-NYC, for instance.
Certainly a few bmi regional people I've mentioned it to were surprised.
You can't book on lufthansa.com because the BM flights don't have an LH codeshare, and I'm not sure if there's a baggage interlining agreement in place or not? Opodo, Expedia et.al. do seem to pick it up.
Hopefully with some LH codeshare numbers on the FRA/MUC/HAJ/HAM routes, it'll make it very much more discoverable than relying on
bmi regional alone.