I could not find a specific code reference but I think this is a possibly dangerous install. For now the circuits are the same phase, but for future trouble shooting or renovation work, no one can insure these two circuits will remain on the same phase. if the landlords hot leg is changed and becomes a different phase than the one feeding the lights you will have a 208v or 240v (depending on the service) short at the landlords switch when the lights are on and not knowing he turns them on. this has the making of a dead short across two phases. my solution, and i have used them before is a dual element fixture. one element controlled by tenant space, one by landlord. they work great for energy conservation, but would work in this application also.