updated jsfiddle to https://jsfiddle.net/9oqvcqd1/20/ to support Edge, and any other browsers that do not support Element.prepend().

Blink>Input might be better for mouseleave.

You are correct in what you expect here however I'm not able to reproduce it.

Are you able to provide us with a Input Latency trace from: chrome://tracing 

Have you tried this on different hardware? One explanation of such behavior is sometimes some hardware will generate phantom touch moves and if the touch position differs from the mouse position you'd see something like this.

Sure. Heads up, this is my first filed chrome bug, and my diagnostic knowledge of the sub-system is garbage.

I tested a single system with 2 input devices.
- Logitech 810-002182
- Microsoft X08-71118

They are cheap mouses, but they have a wide distribution.

I included 2 traces per mouse,
- input-only: was recorded under the requested 'input latency' profile
- full: was recorded with extra features that may be helpful such as, blink, event, ui, v8, etc.

I made sure that each trace includes several invalid mouseleave events, but they will also have 1 legitimate mouseleave where the mouse exited the demo target to terminate the recording.

If these traces are not helpful I can test another system.

Deleted: trace_mouseleave-Logitech-input-only.json.gz 1.1 MB

trace_mouseleave-Logitech-input-only.json.gz 1.1 MB Download

Deleted: trace_mouseleave-MS-input-only.json.gz 1.4 MB

trace_mouseleave-MS-input-only.json.gz 1.4 MB Download

Deleted: trace_mouseleave-Logitech-full.json.gz 1.6 MB

trace_mouseleave-Logitech-full.json.gz 1.6 MB Download

Deleted: trace_mouseleave-MS-full.json.gz 1.3 MB

trace_mouseleave-MS-full.json.gz 1.3 MB Download

Thank you for providing more feedback. Adding requester "dtapuska@chromium.org" to the cc list and removing "Needs-Feedback" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

2 more important points:

1. I was able to recreate this bug in Edge today.
2. The speed of these mouse clicks is frantic, however, this report started with a list similar to my demo that was hiding itself on mouseleave. Very normal paced clicking in the list was causing spurious mouseleave events and causing the list to hide. So under different circumstances, the pace of mouse events is not an issue.

Sounds to me this is a hardware issue. You might examine the native OS windowing events using something like Spy++. Since it is reproducible in Edge as well there isn't much we can do.

The trace clearly indicates that a mouse leave is being generated but isn't from a touch event. 

I wonder if you have any software that is generating these phantom leaves. Have you tried removing any non-standard software (like logitech drivers/plugins).

The NextAction date has arrived: 2017-08-31

I also tested this and couldn't reproduce the issue on the latest stable. Closing this for now. Feel free to file a new bug or comment on this one if you found a more reliable way of producing this.