Thank you for the screencast.  I was not able to reproduce this issue, unfortunately.  Would you happen to have an open source code that could help us investigate?

Hi, this issue reproduces if you try to see in a tooltip large method.
As you see from videos 6s if method content is large it shows 2nd tooltip right above first tooltip and triggers focus out for first one which causes its to disappearance. It is likly to reproduce when dev tools window has reasonable small height like in video.

Thank you for providing more feedback. Adding requester "luoe@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

Oh!  I see what you mean, I can now reproduce it with a long function name and relatively small DevTools window dimensions.  I'll take a look.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c68fece6362635a1d14b92c54f330f12d2998e47

commit c68fece6362635a1d14b92c54f330f12d2998e47
Author: Erik Luo <luoe@chromium.org>
Date: Tue May 29 18:41:09 2018

DevTools: avoid covering or hiding popover when tooltip is shown

- Adds 'pointer-events: none' so that hovering a tooltip does not
  cause a popover to blur and disappear.
- Accounts for cursor offset when positioning a tooltip above the
  cursor.
- Trims function tooltips everywhere to 500 chars.

Screenshots:
https://imgur.com/a/8mfMGXA
https://imgur.com/a/aWsRsKX

Bug:  806194 
Change-Id: I64a479aa5d93b10ade286d59957c52df4997851c
Reviewed-on: https://chromium-review.googlesource.com/1072738
Commit-Queue: Erik Luo <luoe@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562521}
[modify] https://crrev.com/c68fece6362635a1d14b92c54f330f12d2998e47/third_party/blink/renderer/devtools/front_end/object_ui/ObjectPropertiesSection.js
[modify] https://crrev.com/c68fece6362635a1d14b92c54f330f12d2998e47/third_party/blink/renderer/devtools/front_end/ui/Tooltip.js
[modify] https://crrev.com/c68fece6362635a1d14b92c54f330f12d2998e47/third_party/blink/renderer/devtools/front_end/ui/tooltip.css

luoe@ - Could you please provide a sample test file/url to verify the issue from TE-end.

Thanks...!!

Sure, here's a repro:
- Open DevTools
- Navigate to https://jsfiddle.net/rdgv2vmj/
- Once DevTools is paused on the 'debugger' line, scroll the code editor until the `function abcdefg()` text is close to the bottom of the window: https://imgur.com/a/VQGE4pC
- Hover the mouse over the function name `abcdefg` until a popover appears
- Hover the mouse on the `f abcdefg` in the popover body, and wait for a gray tooltip to appear

Actual: Upon hovering over the popover body, the tooltip may appear for a few frames then the popover will disappear
Expected: Popover should remain visible

You can also see the repro in action in this: https://imgur.com/a/8mfMGXA

Hope this helps