Steps to reproduce:
Use the Bulk Add/Remove Labels script to add the label "FOOBAR" to a bunch of pages in the space.
Immediately change the action to "Remove label" and run the same script.
The label you just added is removed.
You receive the message,
"No pages need updating for the chosen labels and pages."
This seems to be because the add action, just like Confluence, automatically lowercases all labels, but the comparison to remove them does not.