Onscroll event handling is handicapped by right-clicking the Flash plugin. Post right-click, events are only received on the scrollbars mouse release. Other browser events continue functioning properly. Example: http://www.leefernandes.com/safariBug
Confirmed with a local debug build of WebKit r25168 with Safari 3 Public Beta v. 3.0.3 (522.12.1) on Mac OS X 10.4.10 (8R218).
Safari 2.0.4 (419.3) with original WebKit on 10.4.10 has the same behavior, EXCEPT it updates the onscroll value properly while scrolling down the screen (dragging the scroll bar down) AND while the Flash movie is partially off-screen.
<rdar://problem/5425573>
I am going to mark this as "RESOLVED WONTFIX" because I don't think there is any intention to improve or bring back NPAPI and any event handling related to plugin. Please reopen, if it is not about NPAPI etc. Thanks!