Assertions:
In all versions of Netscape, if no SRC attribute is initially specified, the frame area is no longer addressable as a target (even if a NAME is specified) for document links, etc. Internet Explorer and Opera handle the case of an initial blank SRC just fine.

Hyperlink to top/right frame (frame initially contains a document)
Hyperlink

Hyperlink to bottom/right frame (frame initially contains no document)
Hyperlink