Go to Adminstration -> Pedigree Editor
Under the Date Format heading, set both values to dd-mm-yyyy (see attached screenshot)
Create a new family and edit the pedigree
For an individual in the pedigree, start entering the birthday. For the year, choose a decade, e.g. 1990s.
The error in the attached screenshot is displayed in the JS console
After saving and re-opening the pedigree, it is displayed without lines connecting the nodes.
This might be a duplicate of PT-3446.