The Leoteks on the freeway here sometimes droop from vibration/shock too. I've seen it happen to wood pole lights too. Makes me wonder if the bolts weren't tightened enough or if they were overtightened. Each brand specifies a specific fitter bolt torque (it varies by brand) but I've never seen any electrician use a torque wrench to tighten ANYTHING, certainly not slipfitter bolts.