There are issues with the label editor, related to the batch_id: 1/ You can select all the items and click on "remove selected" without any warning 2/ You can delete the last item clicking on the "Delete" button ("actions" column) In these 2 cases, the batch_id parameter is passed but is wrong. If you add a new batch on the resulting screen, the batch_id of the deleted batch will be displayed, but a new one will be used. Copied from the comment by Jonathan Druart on Bug 15663 https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=15663#c7
My understanding of the bug report is this: If you remove (by "remove selected" or the delete button) all items in an existing label batch and then immediately add new items to the batch, the batch will be saved with a new batch_id. In my test this was not the case, so I'm closing this report. If someone finds otherwise please re-open with more details.