Repro steps:

1. elastic-package stack up
2. Install the package you're developing - Fleet adds a Managed and <package name> tag to the dashboards by default
3. Make changes to dashboard
4. elastic-package export dashboard -d <id> will export the tag automatically created by Fleet
5. Now there's a tag in the package and one created by Fleet, which will result in duplicate tags of the same name when a package is installed later

In integrations repo, file search against "kibana/tags" and you'll see packages with the Fleet-created tags exported: