For a Non-Identifying Relationship, erwin allows you to change the Null options from 'Nulls Allowed' to 'Nulls Not Allowed'. It also changes the Null option for the Column from 'Null' to 'Not Null'. You can then go to the Column editor and change the 'Not Null' back to 'Null'. However, that does not change the nullability in Relationship editor which still shows 'Nulls Not Allowed'. Why this inconsistency?
This is by erwin design to provide users more flexibility for modeling. In general it is correct that the nullability option in Relationship editor should be same as in the Column Editor. After all, if a Relationship is marked as 'Nulls Not Allowed', then how can a column be marked as Null without changing the nullability in Relationship editor as well? However, it is true only if a PK comprises of just one column. Consider the scenario where there are more than one column as part of the PK. In that case, by default all columns will migrate to the Child Table as FKs. What happens if a user wants just one of those FKs to be Not Null and not all columns. See the image below:
Default behavior (see the Nullability)
After changing the nullability in Relationship editor (see nullability changes to 'Not Null' for ALL FKs.
Now, if you want to change the nullability of just two columns, you can do so in Column editor to show it as follows:
This is only possible if there is a flexibility of overriding the nullability in Relationship at the Column editor.