Mass update not working on Report page for Campaign

I'm trying to update a field based on which users have clicked on a campaign. There is an option to choose "Mass Update" and then choose a field to update. I have created a field called "followup" and I mass-update this field to "true." I get a popup saying the update was successful.

Then I go to the Segment that is supposed to show all contacts with "followup" as "true." No contacts have been added. The mass update has not worked.

Note: I can't use the "Email clicked recipients" feature because some of the people who clicked actually went on to order the product, and I don't want a followup email sent to those people who already made the purchase. By using a Segment, I can then go in and delete the recipients who already ordered.