Avoid duplication of messages in search

Hi folks,
Have a problem with the setup of streams and indexes.
Using version GL 3.2
I use 2 indexes default and app_data.
I created a new stream ApplicationData using index app_data removing matches from ‘All messages’ stream.
This stream ApplicationData has one rule Field z_category must match exactly HISTORY.
Messages are stored in both indexes. That is fine.
While searching via the REST API, I am observing duplication of the matched messages.
I decided to filter searching by stream in query z_category:HISTORY AND streams:5ec8530948... to eliminate the duplication.
It didn’t help. I have noticed that messages from the default index have assigned 4 streams and include also my ApplicationData stream 5ec8530948…
I found it weird. Why my ApplicationData stream 5ec8530948… is assigned to both indexes? (I set just one)
Can I remove my ApplicationData stream from the default index? How?
How can I manage the indexes of a stream? It looks like just one index should be assigned to a single stream in UI.
Is there any workaround? to get rid of duplication. Thanks for any advice.

There is something wrong with your streams. I have many of them, routing messages to respective indices, and there is no duplicates at all.