We have created two collections under Recommendations-Collections in adobe target. Both are currently using the Development environment.
However when I change the environment of one collection from Development to Staging, then it automatically updates the environment of the other collection from Development to staging.
This is not a bug, however is working as designed. This environment setting is basically giving a preview of the entities present in the catalog for that environment. The configuration sticks to the last selected option when moving from one collection to another in UI.