Confusing popups when importing activities

This is on CiviCRM 5.24.1, just installed. The behavior of the Import Activities page is odd. On the Preview page, Step 3 of 4, the buttons Previous, Import Now, or Cancel are displayed. However, no matter which button is selected, a popup box says: "Backing up your database before importing is recommended, as there is no Undo for this. Are you sure you want to import now?" Then the import appears to start and a progress bar appears, even if Previous or Cancel were selected. If Import Now was selected, the import proceeds normally. If Previous was selected, nothing is imported, and it returns the user to Step 2 of 4. If Cancel was selected, nothing is imported, and it returns the user to Step 1 of 4. No harm is done, and the return to previous steps is correct, but the popups give the appearance that we are unable to stop the import regardless of the option selected, which is alarming to the user. This behavior is confirmed on the demo site.