[Webkit-unassigned] [Bug 141116] New: Mousemove event is not firing as intended

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=141116

            Bug ID: 141116
           Summary: Mousemove event is not firing as intended
    Classification: Unclassified
           Product: WebKit
           Version: 420+
          Hardware: PC
                OS: Windows 8
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: HTML Events
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: wowmotty at gmail.com

Created attachment 245781
  --> https://bugs.webkit.org/attachment.cgi?id=245781&action=review
CPU Profile of 12 image demo

I apologize in advance for not being able to determine the exact issue here, or provide a reduced test case.

Overview: Essentially, this is was found while using the jQuery AnythingZoomer plugin. There is a significant delay (2-3 seconds) that is introduced when trying to position a div containing more than 10 stacked images under the cursor; with 10 or less images the behavior is as expected. This issue does not occur in Firefox, Opera or IE11 (I didn't test in older IE versions).

Here is a demo of the plugin behaving as expected (10 images in large container): http://jsfiddle.net/5j354atc/3/
Here is a demo of the huge delay (12 images in large container): http://jsfiddle.net/5j354atc/2/

Steps to Reproduce:
1) Load the demo; there is an expected initialization delay of a second or two.
2) Move the mouse anywhere over the map.
3) Notice how long it takes for the zoom window to appear under the mouse.

Actual Results:
In the 12 image demo, I ran and profile and examined the flame graph (CPU profile attached). I noticed that jQuery was not receiving any mousemove events

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