Vertical split line disappears in diff mode with relativenumber

[yamam]

Problem

In vertical split diff mode with relativenumber set and one window maximized, the vertical split line partially disappears.

Steps to reproduce

nvim --clean --cmd 'set relativenumber'
10aa<CR><ESC>gg
:vnew
ab<CR><ESC>gg
:difft
<C-w><C-w>
:difft
<C-w>|j

Vertical split line disappears.

Expected behavior

In nvim 0.9.5
Vertical split line doesn't disappear.

Neovim version (nvim -v)

NVIM v0.10.1-dev-53+g17fe405ad

Vim (not Nvim) behaves the same?

no, vim 9.1

Operating system/version

Ubuntu 24.04

Terminal name/version

GNOME Terminal 3.52.0 using VTE 0.76.0 +BIDI +GNUTLS +ICU +SYSTEMD

$TERM environment variable

xterm-256color

Installation

build from repo