Setting mapping in `cmp.setup.cmdline({'/', '?'}, {` prevents command tab completion from working after search

FAQ

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

Announcement

• I have checked Breaking change announcement.

Minimal reproducible full config

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/cmp-cmdline'
Plug 'neovim/nvim-lspconfig'

Plug 'hrsh7th/cmp-path'
Plug 'hrsh7th/cmp-calc'

call plug#end()
PlugInstall | quit

" Setup global configuration. More on configuration below.
lua << EOF
local cmp = require "cmp"
cmp.setup {
  mapping = {
    ['<CR>'] = cmp.mapping.confirm({ select = true })
  },
  sources = cmp.config.sources({
    { name = "nvim_lsp" },
    { name = "buffer" },
  }),
}
local capabilities = require('cmp_nvim_lsp').default_capabilities()

cmp.setup.cmdline({'/', '?'}, {
    -- setting mapping causes the issue of :e %^I after / search
    mapping = cmp.mapping.preset.cmdline(),
    sources = {
        { name = 'buffer' }
    }
})
EOF

Description

When mapping = cmp.mapping.preset.cmdline(), is provided to the /, ? cmp cmdlines, after searching once tab completion in the vim commandline stops working and prints ^I instead. If you remove the mapping then the problem won't trigger.

Steps to reproduce

1. Open some file with nvim using attached minimal config
2. Verify that :e %<tab> will actually tab-expand % to current filename.
3. Perform search using /foo<CR> or equivalent; verify that :e %<tab> will not work anymore and instead, print ^I per tab invocation.
4. Comment out mapping line in example config and verify (3) above cannot be reproduced.

Expected behavior

:e %<tab> will expand current filename after performing at least one search

Actual behavior

:e %<tab> will expand to :e %^I which is not expected.

Additional context

I don't know the significance of the mapping attribute for the search cmdline config but I merely copy-pasted it from the reference manual/README.