Projected light emitter must be in a _linked_ object and rotating with PRIM_OMEGA or the like. Note that particles, a similar viewer-side effect, do _not_ drift. This is not a server-side bug: no active script need remain in the object for the drift to continue. See https://community.secondlife.com/forums/topic/507574-projected-light-slowly-drifts-from-targetomega-use for video, sample setup script, detailed observations