(The below is not a real TOC, please don't attach it!)
This is a very confusing result. It displays a release (group?) as a possible match, but no mediums. I think this is happening because the RG has a "partial" match. It was a release with a medium with the right number of tracks; but the medium type is "Digital Media" so it cannot have a TOC attached to it. If the medium was type CD or no medium type the match would be displayed. If the RG had no mediums with the same track #s you wou'dn't see it as an option.
If you click "Attach CD TOC" it does nothing (which is better than an ISE!) - but no error message (e.g. no release selected)
Release (groups) that were deemed to have no compatible mediums should not be shown as a possible match (which brings us to