Steps to reproduce:
1. open User's attached project
2. Assets - Create - CreateAssetsList
3. name newly created object as "abc"
4. select "abc" and and choose Create Child Asset from the Inspector. Press CTRL+S and you will see that it will create a new asset and add it to the parent's hierarchy. Note that this asset will have the same name as its parent

Result: the child asset has been added as a Parent asset instead of being added as a Child asset (you can confirm it as the new asset will have an IAction script with some fields in the inspector).

Note:
-rename "abc" to "zzz". Notice that this has changed both Parent's and Child's names to "zzz" and also changed their places (now Parent is in the place as it should)
-now rename "zzz" to "cde". Notice that this has only changed Parent's name
-with 5.5.0b2 and 5.4.1f1 when doing steps 4 there is no name given for child thus the issue does not appear
-User is using AssetDatabase.AddObjectToAsset() method

Reproduced with: 5.4.0p4, 5.3.6p2, 5.2.5f1