Created attachment 272761 [details] Bug Video The handle is offset. This happens in Frames and Events mode. See video.
<rdar://problem/24955855>
The start handle is fine.
Likely related, zooming the timeline causes the end handle to move disproportionally to the zoom scale. The Start handle is fine. See second video.
Created attachment 272764 [details] Zoom Bug Video
Fixed by https://bugs.webkit.org/show_bug.cgi?id=154971.