I've recently published this post in Wikidata Project Chat:

I think there is an issue with one of the constraints. I've just added Wawrzyniec Żuławski (Q2713080) as the child of Jerzy Żuławski (Q1373117). In this case the son was born on 14th Feb, 1916, while his father died on 9th Aug, 1915. This triggered warning caused by Q25796498 constraint. As we obviously all know, human pregnancy is usually ca. 9 months long, so it was entirely possible for the child to be born 6 months after the father's death. I think the constraint should be fixed to reflect such situations.

The reaction of other users was that is a frequent problem, which should be reported to developers using Phabricator. So here I am :)