Border with `side_padding=0` adds two empty rows in compl menu

[GordianDziwis]

FAQ

• I have checked the FAQ and it didn't resolve my problem.

Announcement

• I have checked Breaking change announcement.

Minimal reproducible full config

if has('vim_starting')
  set encoding=utf-8
endif
scriptencoding utf-8

if &compatible
  set nocompatible
endif

let s:plug_dir = expand('/tmp/plugged/vim-plug')
if !filereadable(s:plug_dir .. '/plug.vim')
  execute printf('!curl -fLo %s/autoload/plug.vim --create-dirs https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim', s:plug_dir)
end

execute 'set runtimepath+=' . s:plug_dir
call plug#begin(s:plug_dir)
Plug 'hrsh7th/nvim-cmp'
Plug 'hrsh7th/cmp-buffer'
Plug 'hrsh7th/cmp-nvim-lsp'
Plug 'hrsh7th/vim-vsnip'
Plug 'neovim/nvim-lspconfig'
call plug#end()
PlugInstall | quit

" Setup global configuration. More on configuration below.
lua << EOF



local cmp = require "cmp"
cmp.setup {

window = {
  completion = {
    border = {
      '▗',
      '',
      '▌',
      '▌',
      '▘',
      '',
      '▝',
      '▐',
    },
    side_padding = 0,
  },
},

  snippet = {
    expand = function(args)
      vim.fn["vsnip#anonymous"](args.body)
    end,
  },

  mapping = {
    ['<CR>'] = cmp.mapping.confirm({ select = true })
  },

  sources = cmp.config.sources({
    { name = "nvim_lsp" },
    { name = "buffer" },
  }),
}
EOF

lua << EOF
local capabilities = require('cmp_nvim_lsp').default_capabilities()

require'lspconfig'.cssls.setup {
  capabilities = capabilities,
}
EOF

Description

Vanilla:

With this setting for completion window:

window = {
  completion = {
    border = {
      '▗',
      '',
      '▌',
      '▌',
      '▘',
      '',
      '▝',
      '▐',
    },
    side_padding = 0,
  },
},

There are two additional rows:

Steps to reproduce

Insert aaa repeatedly.

Expected behavior

No additional rows.

Actual behavior

Two additional rows.

Additional context

No response