Hi. I've just noticed this, so I'm not sure it's always been there or it's appeared with latest Omeka releases... I'm using Omeka Classic 3.1 and Multilanguage 1.6.0
When editing an Item or Collection, after pressing Add Input button to add extra info to a specific DC field, the page reloads with just the info already available for that field; all previous and following fields are not displayed. When saving, the information get correctly saved and all fields are displayed again.
Let me know if you need more details.