This is the most logical explanation though Its a hard pill for me to swallow. There is a open breather in the opposing valve cover leaving another place for air to come in besides the tube. I would think the breather would be less resistant entry point. Non the less it is the only logical explanation.
The blm would prolly react similar if the pcv was removed. All the unmetered air that comes through the pcv would come through the maf. Maf number would slightly increase and blm would slightly drop. At least that’s what logical thinking suggests.