Why i get duplicate asset when i import updates packages?

Dear community recently i make Augmented Reality using Vuforia.
The markers on vuforia downloaded as Unity Packages.

First, i have 3 marker, i can import the packages the normally.
But when i add new marker and try to import updated packages to Unity 5.1.1f1, the marker have duplication?
How to avoid duplication on import Unity packages on Unity 5.1.1f1?

 

Its a new behavior in unity that should prevent you from accidentally overwriting your files.
Just go into a empty scene, delete the old marker data files, import the new one, and then you can go back to yoUr normal scene.
Changing into a empty scene prevents your scene with the scripts to lose the reference to the markers.

 

Delete old asset? the final result of old scene is become assetBundle sir. If i delete, how unity detect i make updates of the bundle?
I have been trying if i delete the old asset the project broken