This happens only under some conditions, the problem does not happen when a patient record is manually unlinked.
create simple pedigree mother-father-child
add genes, phenotypes, diagnoses and cancers to all 3
now modify all the info for all 3 nodes and add a brand new node with cancer, diagnosis, phenotype and genotypes, DO NOT Save
import exported pedigree
the pedigree looks accurate; there is a family member that isn't linked
create a new node and drag this family member to it --> PROBLEM: all cancers are gone (but genes etc. stay)