SVN 4135. Was tempted to put born again children in the subject.
Anyway, after merging two parents and their FAM, I began merging the children. It seemed that some of them worked properly, but at least one "from" child's INDI key was changed to the TO instead of being deleted (leaving the same person as child twice. And at least three of the "from" children had their INDI records merged correctly, but the old keys remained in the FAM pointing nowhere.