Labels get lost during export and import to another Bamboo instance

We export our 140 Bamboo buil plans to a ZIP file with the built-in export functionality periodically and import it to a test instance of Bamboo with the build-in import functionality.
All the build plan labels get lost during this transfer, which means at least an hour of work to recreate the labels manually.
The labels itself get exported to the file db-export/labels.xml correctly, but I cannot find any other occurrence of the label id or the name in the exported files.