Hi, must admitt I had this problem, 6 of my 10 seeds 'cracked' no problem, as I germinated in rockwool I originally thought (my first grow) they hadnt germinated but 7 days after the others had sprouted curiosity got the better of me and I investigated very carefully with a steralised scalpel into the rockwool. 3 of the remaining seeds had cracked but appeared to be 'stuck' so I very, very carefully knocked of the casing. Those seedling are now doing fine if only 5-6 days behind the other six.
I am a nood but my experience as long as your very careful and sterilise what ever your using it was cool with me
cheers bill