If I try to upload a file with a 250-character ASCII filename, the Upload Wizard allows me to submit the form but then the upload fails. If I click "Back" and then "Next" I can get back to the file description stage, but with no indication of which files failed.
Start the Upload Wizard. Click "Select media files to share", choose a file, then "Add more images" and choose another one. Click "Continue".
On the next page ("Release rights"), click "These files are my own work". Click "Next".
On the next page ("Describe"), completely fill the "Image title" box for one image with 250 ASCII characters. Write a short title for the other image. Also provide a description and if necessary a date for each one. Note that there is no indication that the long title is a problem. Click "Publish".
The next page will indicate that one upload has succeeded and the other has failed, with a message "Filenames may not be longer than 240 bytes." Click "Back".
This will return you to the "Release rights" page. From there if you click "Continue" you will be returned to the "Describe" page, but there will be no indication which files need their names shortened and which have been successfully uploaded.
What should happen is that (a) the "Describe" page should reject excessively long filenames and (b) there should be a better recovery route when uploads fail.