Top-level tag descriptions are lost after combining

[Ghazgkull]

OpenAPI 3.0 supports a top-level tags element which can be used to provide descriptions for tags as well as setting the order of tags for editors.

This support is explained here in the section which says:
Optionally, you can specify description and externalDocs for each tag by using the global tags section on the root level. The tag names here should match those used in operations.

When I combine two openapi yaml files containing top-level tags, this information is completely lost.