It happened repeatedly a couple of years ago, and I just found it again yesterday. Looks to me like blocking up the easier holds to make the traverse harder. Again, may not be climbers, but I can't think of anyone else who might do this? It looks a reasonably time consuming job to find rocks the right size to bash into each of the pockets (it's certainly a bit of work getting them back out as they are tight fitting). And I've only found the holds filled in on the two climbing traverses (the warm up under the big roof and the traverse / sit start problems around LSD etc.)