Richard, I've seen crud and experienced the results (OAK#1 comes into mind, quite impossible with Starters). This hole, BPB #13, also has a crud area, see the front green camera.
MB, there may be only a small patch of "fringe" - I only found it from the perspective view of my replay.
I never made up a connection between the crud and this patch of fringe - maybe this is the solution of this mystery :)
BTW, is crud a word known on real golf courses?