some strains just do. 12 hours doesn't feel the same to all strains. very strange you said that because i'm talking to another guy with the same prob. put it under 24 if you want to veg it. and if you choose to grow many plants of this strain only a few might have that flaw and could mess you up. i'm doing an auto strain right now and yours could have been croosed with 1. either way not genetics you want unless they all do that in a stable manner. otherwise try a new strain. thats what hes doing. good luck man