Editing of frame's attributes.
You can edit attributes of the current frame (size, offset, transparency, local palette, interlacement, delay, title, "How To Remove") by means of menu item Image / Attributes or on tab Image of Attribute Toolbar. Button allows you to assign attributes of selected image to all images checked in the List of images.
The default attributes are assigned to images that don't contain settings. This situation is occured if you add any image to your GIF as a new frame (including GIF- file created by another application). Default settings may be redefined in the File / Preferences dialog.