bug#42655: 27.1; iconify-frame on a Lucid build may stuck the frame

[Eli Zaretskii]

> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Sat, 01 Aug 2020 20:46:03 +0200
> Cc: paul eggert <eggert@cs.ucla.edu>, stefan monnier 
> <monnier@iro.umontreal.ca>,
>  uyennhi.qm@gmail.com
> 
> In a GUI session, with Emacs built with Lucid toolkit in a Linux machine,
> do:
> emacs -Q
> C-z
> ;; select again the window displaying the Emacs GUI
> -------------------------------------------------------------------------------
> 
> - You cannot insert characters in the *scratch* buffer.
> - Normal movement, for intance, `C-n' or `C-f' doesn't work.

If you now attach a debugger to Emacs, what does the backtrace show?