Reproduction Steps:
1. Have a catalog with more than 1 item in it.
2. Click New Store
3. Give the store an ID and click "Add To Store"
4. Search for something that will identify just 1 item out of the N items that you have
5. Click Add All
6 Observe that N items were added, instead of just 1.
Expected behavior:
This behavior really limits the usefulness of filtering, if you filter down to a list of 100 items you are going to have to click 100 times per store per bucket (if you are split testing) to be able to manage that data or build your own solution. Seems pretty onerous.
