Test case:

1. Select in UW a file with a filename like "Test1234.jpg"
2. Continue to tab "release rights" and select "own work"
3. Continue to tab "Describe": Change the "Image title" from "Test1234.jpg" to "Test1234#.jpg"
4. Click on "Publish"

Nothing happens. No UI error message about the (now) invalid image title. Upload is impossible.

Firefox console throws:

jQuery.Deferred exception: extension is null Title.normalizeExtension@https://commons.wikimedia.beta.wmflabs.org/w/resources/src/mediawiki.Title/Title.js?d684a:749:4
uw.controller.Details.prototype.valid/</promise<@https://commons.wikimedia.beta.wmflabs.org/w/extensions/UploadWizard/resources/controller/uw.controller.Details.js?d4610:192:38
mightThrow@https://commons.wikimedia.beta.wmflabs.org/w/resources/lib/jquery/jquery.js?6a07d:3534:21
resolve/</process<@https://commons.wikimedia.beta.wmflabs.org/w/resources/lib/jquery/jquery.js?6a07d:3602:12
undefined

Suggestion: Normalize the image title after every manual change.