I was using UploadWizard to transfer some files to Flickr. During the description step, I filled in Captions (and other elements), and reached the upload step.
The following happened:
“Something went wrong with uploading captions”, leaving the UploadWizard in that state − it was not possible to move forward to the next step (the ThankYou and the list of files uploaded), nor to move back to the previous step.