Until now each image was rendered with a title attribute. This title was either the image meta "title" or if empty the title of the image module itself. The was no chance to have an image without any title (mouse-over) attribute.
We now added a separate setting for this image (mouse-over) title and only generate a title attribute if this field is filled.
To be backwards compatible we still render a title if the title setting is null (not defined) so "old" images are unchanged. If you edit and save an image module, the title will be an empty string and then no title will be rendered.