Initial prompt invisible (regression in 5.4.1)

[Ruud van Asseldonk <ruud@xxxxxxxxxxxxxx>]

Hi,

After upgrading from Zsh 5.3.1 to 5.4.1, the initial prompt is sometimes
not painted when I open a gnome-terminal window. See screenshot here:

https://imgur.com/a/vBDyL

There is a single text-colored pixel in the terminal at the normal
location of the cursor.

When trying to take a screenshot of this, I noticed that the prompt is
painted when the window loses (or gains, I am not sure any more) focus,
if it was not painted initally.

This does not happen consistently, it happens about 1 in 4 times when I
open a new terminal. It seems a weird issue to be a Zsh bug, but after
downgrading to 5.3.1 I have not observed this issue again. When
upgrading to 5.4.2 later I did observe the issue again.

Last known good version (of Arch package): zsh-5.3.1-2
Known bad versions: zsh-5.4.1-1, zsh-5.4.2-1

My zshrc is here:

https://raw.githubusercontent.com/ruuda/dotfiles/master/zsh/.zshrc

I did customize the prompt near the end.

Let me know if there is anything I can do to help diagnose this issue.

Kind regards,

Ruud