wrong_window_size.vim

function! SpawnBufferWindow(name)
    let dummy_buf = bufnr(a:name, v:true)
    call setbufvar(dummy_buf, '&buftype', 'nofile')
    call setbufvar(dummy_buf, '&bufhidden', 'hide')
    call setbufvar(dummy_buf, '&swapfile', 0)
    call setbufvar(dummy_buf, '&buflisted', 1)

    execute 'belowright vertical split #' . dummy_buf
endfunction

split dummy_preview
resize 2
set winfixheight
set winfixwidth

wincmd j

call SpawnBufferWindow('dummy_buf')

wincmd h

call SpawnBufferWindow('dummy_buf_2')