This is neat! These are tandem breakers being used as two pole breakers for baseboard heating circuits. They just alternate the black and white conductors between the two breakers to split the phases. Kinda hard to get a common trip though?
Common trip or handle ties are required so the correct CB’s should be installed.
See Robert’s post
Indeed. Was this an accepted practice in the past? I didn’t think so. It is hard to believe this passed a final inspection.