Subject: bug#27647: 26.0.50; Line numbers implemented natively disappear momentarily when frame out of focus

From: Eli Zaretskii <[email-masked]>
Date: Thu, 05 Oct 2017 16:39:53 +0300

> From: Eli Zaretskii <[email-masked]>
> Cc: [email-masked], [email-masked],
> 	[email-masked]
> 
> It's most probably something related to some hook or timer that you
> set up in your customizations.

Or maybe some feature calls kill-all-local-variables, but doesn't
restore display-line-numbers until later.