Image field images cannot be removed

Created new content type, set image field. All images uploaded can't be removed by clicking remove button. If you click it, page reloads, if you click it twice, image disappears and I get message that node has been updated but you can't save page anymore because Drupal tells me that page has already been modified.

"The content on this page has either been modified by another user, or you have already submitted modifications using this form. As a result, your changes cannot be saved."