Go to the above link. Scroll the main frame down a bit. Reload. The main frame is now scrolled to the top, but it should be scrolled as it was before reloading. If you perform the same test without frames, the scroll location is maintained. Curiously scroll state is maintained if you navigate away and then come back to the frameset (going back to a page and reloading it are fairly similar). 10.4.7 and tot as of r15648 behave the same way. I wouldn't be surprised if this is a regression from some point in the 10.3 era.
I will be checking in some automated tests that are blocked by this bug. When fixed, look through LayoutTests/http/tests/navigation/*disabled for this bug number.