These 2 iframes are completely separate, setting the src directly. Firebug's net tool indicates that only one request is made for dummypage2.html

This is similar, but the iframe src are set in JavaScript

Donkey

This iframe has src of the first frame above - but it appears blank

Here is some text in a DIV

This iframe has src of the preceding DIV - but it is also empty :-(

This iframe has no src initially, but gets it altered by JavaScript

Debug text appears here