The issue has been closed
It looks like at some point GitHub added a click area in the blank part of the header, right in the middle, that triggers the search opening.
It is pretty annoying to me but I wanted to open a discussion first to see if anyone else is bothered by it before doing more.

GIF or Video of what you are referring to?
posted by yakov116 almost 4 years ago
posted by Stanzilla almost 4 years ago 
This does not happen to me in chrome on windows
posted by yakov116 almost 4 years ago
Same on Safari, nothing happens when clicking outside
posted by fregante almost 4 years ago
That is weird, I can repro without any browser extensions even on Chrome 92.0.4515.51. I will test with more browsers.
posted by Stanzilla almost 4 years ago
I managed to repro consistently in a fresh Chrome 91 profile (having login to github) in the following way:
rightclicking on the middle of the blank area of the header, then immediately leftclicking
(the mouse has to be in a specific vertical position, otherwise it doesn't occur)
and finally pressing Esc, and repeat:
<details>
<summary>screen capture</summary>
<!-- leave a blank line above -->

</details>
posted by darkred almost 4 years ago
Please report this to GitHub
posted by fregante almost 4 years ago