Steps to reproduce:
* go to a File page that has a statement with qualifiers (e.g. https://commons.wikimedia.beta.wmflabs.org/wiki/File:Photo_on_20-06-2019_at_12.36.jpg)
* click 'edit' on structured data panel showing the statement with its qualifiers
* change one of the qualifiers so that its property has a different type (e.g. if the property has type entity change it to one with type quantity, or vice versa) - but **don't** change the value
* click 'submit'
* you'll see the old value with the new property, and won't be able to edit the panel again (and if you reload the page the qualifier whose property you changed will be gone)