Mark disappears with small updatetime

[petobens]

Consider the following minimal vimrc

set nocompatible

let $DOTVIM = expand('$HOME/.config/nvim')

set runtimepath+=$DOTVIM/bundle/repos/github.com/Shougo/defx.nvim
filetype plugin indent on

set updatetime=500

call defx#custom#option('_', {
            \ 'winwidth': 30,
            \ 'split': 'vertical',
            \ 'direction': 'topleft',
            \ })

augroup ps_defx
    au!
    au FileType defx call s:defx_settings()
augroup END

function! s:defx_settings()
    nnoremap <silent><buffer><expr> <Space>
        \ defx#do_action('toggle_select') . 'j'
endfunction

Now do

1. Open nvim and run :Defx
2. Within the defx buffer select a candidate with <SPACE> -> the candidate mark is shown
3. Wait half a second -> the mark disappears

I expect the mark not to disappear.

[petobens]

Thank you!