That's what happened to a couple of logs of Holly I got, in fact all Holly I've ever got, I think it was cut mid-late spring ( I found it in a log pile from woodland clearance, I didn't cut it) I split and debarked and removed pith and in a day the back split tremendously all over. It was for carving wood so not too much a pain, I filled the splits with woodglue to save as much large sections as possible. If I ever get Holly for a bow I'd be tempted to keep the bark on even if cut late winter, and maybe p.v.a over the bark too, I did this for one piece I found and it seasoned well indoors with no checking at all, but was too knotted and crooked for a bow. I reckon it's one to season slowly, and as a stave not half log.
R.D.