Root bone not desired with Blender export

Hello! there is something that I do not understand with the export and import of SkeletalMesh from Blender to Unreal Engine 4.
**In Blender if I export an armature (FBX 7.4) to Unreal Engine 4 without changing the name of the armature, I end up with this hierarchy in Unreal: **

**On the other hand if I change the name for example Armature1 the hierarchy is not the same and it adds me a bone Root with the name of the armature: **

I work with Blender 2.79 and Unreal 4.21. The export settings in Blender and import in Unreal are the default ones.

If I re-import the files into Blender I do not find any noticeable difference between the two.

If compared the two files via FBX Converter 2013 I get nothing noticeable.

And if I convert the files to FBX 2013 it adds a bone Root with the name of the armature in both cases which makes me say that it is a parameter that was added after 2013

I need the armature hierarchy to remain the same regardless of the name of the object so it does not add any Root bones with the name of the armature. Unfortunately, I do not know the FBX SDK and I do not know if the problem comes from Blender or Unreal Engine 4. I can not grind the parameters I can not find anything conclusive: / I made available the files

Thank you for your answers.