Why are some documents inside document sets shown when filtering for document set meta data?

Question

I have a very strange issue: Two files (excel files) - each belonging to a different document set - are shown within the top level view when using a specific Key Filter setting which should only be relevant to the document sets in my library.

Document Library Settings (Content Types)

Simplified, I have a document library with the following two content types

• Basic Document Set
  • Content Type: Derived from "Document Set"
  • Column "Relevance Status"
    • Type: Managed Metadata (points to a very small and flat taxonomy: {Active, Historical})
• Basic Document
  • Content Type: Derived from "Document"

Document Library Content

Based on the above content types, my document library looks as following:

DocumentationA
DocumentationA/FileA.xlsx
DocumentationB
DocumentationB/FileB.xlsx

• DocumentationA and DocumentationB are both document sets of type "Basic Document Set"
• FileA.xlsx and FileB.xlsx are both documents of type "Basic Document"
• DocumentationA has a "Relevance Status" set to "Historical"
• DocumentationB has a "Relevance Status" set to "Active"

Metadata Navigation Settings

Since I want to hide/show certain document sets using the "Relevance Status" , I have configured this field as "Key Filter Field" with an automatic index creation.

Issue: Filtering shows unrelated files

When I filter the documents using the "Relevance Status" "Historical", only the document set DocumentationA appears: This is fine and what I expect BUT when I filter the documents using the "Relevance Status" "Active", the document set DocumentationB AS WELL AS both excel files FileA.xlsx and FileB.xlsx appear. Why?

I cannot see any connection between these files and document sets. Clearly the documents don't have this column I am filtering. BTW: The view settings in Folder are set to Show items inside folders.

Answer 1

The IT department was able to solve my issue with some kind of a workaround:

Removing a default value from the site column avoids triggering this issue.

I was told that the documents inherit the default value of the document set as hidden properties even if they don't have the property defined.