I don't know the cause of the problem, but I do experience a similar issue with Drop Lit Torches OBSE, where sometimes when a torch is dropped it no longer acts as a light source; need to reload Oblivion to fix the issue (more details at http://www.gamesas.com/index.php?/topic/1066588-relz-sm-mod-collection/page__st__100__p__17460345#entry17460345).
I also use All Natural 1.3 which has Real Lights, and OBSE v20; I suspect possibly a combination of some mods causes a subtle race condition that triggers this bug occasionally