That was my first thought so I looked at Texas law. Found 502.409 (Transportation Code) on some law sites but then went to the Transportation Code itself and 502.409 had disappeared. After much research I found that its provisions had been moved to 502.475 but it didn't mention obstructions so I dug a little deeper and found that 502.409 had actually been renumbered, effective January 1, 2012, with a couple of additional words added, as 504.945 and gives a specific exemption for power chair lifts, a couple of other items and "a bicycle or motorcycle rack that is attached to a vehicle in a normal or customary manner."

So bicyclists in Texas can continue using hitch mounted racks without fear of citations (and I'm glad since I have been wanting to get one).