i have had a few break on me before, some on my latest batch. really even though they did that i had no bad problems with it and didnt get a headache from smoking them like some people said they got.
the silver/white stuff people said where so bad on the coals i smoked those ones and they where actually more of a pain in the ass to break than normal ones. gabe says its supposed to be the binder in the coals that keeps them together and considering the ones which had that on them where actually harder to break than the ones without it i would believe it was true.
in the same box i had the silver ones there where weak ones which i could break into quarters with one hand and broke apart when ashing but these where only the top few pieces and it didnt bother me much. other than that the coals i have been getting are just fine.