When a couple's relationship has failed and they begin the process of divorce, emotions often run high. They may harbor ill will towards each other and may occasionally complain, sometimes with a high degree of vitriol concerning their soon-to-be former spouse. This is not unusual or even unexpected.
But in some cases, it doesn't stop. During the divorce proceedings, this parent will continue to comment on the failings of their ex. Some may do it unconsciously, while others may become focused on pointing these failings, real or imagined, out to everyone they meet. And they may point them out repeatedly to the couple's children.