Ah, basically when BM cards aren't "initialized" (which is the case when not previewing or casting) it doesn't process/enable the pass through on the card. I can see that being problematic if you use it during gameplay (when you aren't using a splitter) and the stream loses connectivity in some way.
Is there any way for the card to be always initialized when OBS is launched/idle and if it's a global source? I doubt this can be made to work, but it's a shot in the dark. I don't use this functionality, but I can see how it might benefit Daopa here.