.vimrc

" :TabpageCD - wrapper of :cd to keep cwd for each tabpage  "{{{

" AlterCommand cd  TabpageCD

" nnoremap ,cd       :<C-u>TabpageCD %:p:h<CR>

command!
\   -bar -complete=dir -nargs=?
\   CD
\   TabpageCD <args>
command!
\   -bar -complete=dir -nargs=?
\   TabpageCD
\   execute 'cd' fnameescape(expand(<q-args>))
\   | let t:cwd = getcwd()

autocmd TabEnter *
\   if exists('t:cwd') && !isdirectory(t:cwd)
\ |     unlet t:cwd
\ | endif
\ | if !exists('t:cwd')
\ |   let t:cwd = getcwd()
\ | endif
\ | execute 'cd' fnameescape(expand(t:cwd))
" }}}

execute 'cd' fnameescape(expand(t:cwd))

cd `=expand(t:cwd)`

ではだめですか?

そこはオリジナルのkanaさんのも同じでなんとなくそのままにしちゃったんですよね。
https://github.com/kana/config/blob/master/vim/personal/dot.vimrc (700行目あたり、blobのURLどんなのだか忘れた...)