Save not responding when pasting an image without having right to upload

Reproduction steps:

• Edit CKEditor.EditSheet first JavaScript object to set:

  var uploadDisabled = true; //element.hasAttribute('data-upload-disabled');
  

• Start editing a page
• Drag & drop an image
• Save the document

Expected result:

• Saving the page should work properly
• Maybe the drag & drop should fail

Obtained result:

• Drag & drop is working properly: the image appears in the editor
• When trying to save the notification "Saving" appears and seems to never finish
• The following error is displayed in the javascript console:
  
• After leaving the editor to come back to the image it appears that the page is saved and the image is inserted with a base64 code