Download, build and run project from bug URL (using ToT WebKit). A window with two frames appears, but both frames are empty. With shipping WebKit, they are not empty.
<rdar://problem/5126395>
This looks to be fixed to me. I could not reproduce this with TOT.
I will note that I modified the project to not use the 10.3.9 SDK (I don't have it installed) and corrected a call to -[NSString initWithData:encoding:] which was trying to pass NULL as an encoding (which is an enum). I made it pass UTF8 instead.
Created attachment 16780 [details] screenshot of testcase working on TOT
I also cannot reproduce this anymore (with unmodified project).