Slower zsh prompt in weird circumstances

[Nojus Gudinavičius <nojus.gudinavicius@xxxxxxxxx>]

Hello,

after exploring wayland I noticed that my zsh prompt is flickery. That
is, terminal emulator would render the cursor at X=0, then the prompt
with updated cursor in new frame. This causes flickering visible to bare
eye.

The weird thing is, this happens with only some configurations:
 - zsh
 - zsh --no-global-rcs # my .zshrc is completely empty. --sourcetrace
   only lists /etc/zshenv and my empty .zshrc
But not with:
 - zsh -f # --sourcetrace lists /etc/zshenv
 - zsh -l

zsh 5.9 (x86_64-redhat-linux-gnu)

Thanks,
-- 
Nojus