I made the silliest rookie mistake when I finished this square. Whenever possible I work the ends of colour changes as I go, but on the second round of this square the open mesh did not lend itself to doing this. So when I cut all the ends off at th end of the square I completely forgot this and cut those ends off too without sewing them in.
Needless to say, the block disintegrated within minutes and I had to remake the whole square. It can be found in “200 Crochet blocks for blankets, throws and afghans” by Jan Eaton, on page 60.