Load the testcase I'll attach shortly in Safari for Windows using a current trunk build of WebKit. Make sure the window is small enough so that your page has a scrollbar, and scroll down until the iframe is visible. Right-click in the iframe and notice the context menu appears at the wrong spot. I have not tested on a Mac so I don't know whether this is a problem there. This bug does not seem to occur in Safari for Windows 3.0.4, so it seems like a regression. Some very brief perusal of the code makes me wonder about the way hitTestResultForPoint() passes "true" for the "fixed" parameter when calling absolutePosition(), which seems possibly bogus. But this code hasn't changed in ages.
Created attachment 18380 [details] Testcase demonstrating bogus behavior
<rdar://problem/5682340>
A fix for this was checked in in r29657, so I'm going to assume (w/o retesting) that this is FIXED