Yank para * / + não funciona mesmo com 'gtk-vim'

Question

Editar : estou tentando copiar para a área de transferência fazendo o yanking para * ou + , mas nenhum deles está funcionando. Se eu digitar :reg , não consigo ver nenhum deles atribuído.

Eu já tenho gtk-vim instalado e executando vim --version | grep -e +clipboard retorna o seguinte:

+clipboard       +iconv           +path_extra      +toolbar
sidneyc@nb8395:~$ vim --version | grep -e '+mouse.*' -e +clipboard
+acl             +farsi           +mouse_netterm   +syntax
+arabic          +file_in_path    +mouse_sgr       +tag_binary
+balloon_eval    +float           +mouse_urxvt     -tag_any_white
+browse          +folding         +mouse_xterm     +tcl
+clipboard       +iconv           +path_extra      +toolbar
-ebcdic          +mouse           +smartindent     +xim
+emacs_tags      +mouseshape      -sniff           +xsmp_interact
+eval            +mouse_dec       +startuptime     +xterm_clipboard
+ex_extra        +mouse_gpm       +statusline      -xterm_save

Abaixo, você pode ver meu arquivo .vimrc .

" Encoding
set encoding=utf-8
set fileencoding=utf-8

" Enabling colorful status bar
set t_Co=256
set laststatus=2

" Syntax Highlighting
syntax enable
filetype plugin indent on

" Auto reload file on external change
set autoread

" Indentation
set backspace=indent,eol,start
set complete-=i
set smarttab
set smartindent
set autoindent
set shiftwidth=4
set tabstop=4
set noexpandtab

" Some visual options
set scrolloff=1
set sidescrolloff=5
set display+=lastline
set backspace=indent,eol,start
set listchars=tab:>\ ,trail:-,extends:>,precedes:<,nbsp:+
set title
set background=dark

" Split defaults
set splitbelow
set splitright

" Searching options
set smartcase

" Show line numbers
set number

" Enable mouse
set mouse=a 

" Load plugins
call plug#begin('~/.vim/plugged')
    Plug 'vim-syntastic/syntastic'
    Plug 'flazz/vim-colorschemes'
    Plug 'wincent/ferret'
    Plug 'kien/ctrlp.vim'
    Plug 'itchyny/lightline.vim'
    Plug 'scrooloose/nerdtree'
    Plug 'tpope/vim-fugitive'
    Plug 'tpope/vim-surround'
    Plug 'townk/vim-autoclose'
    Plug 'terryma/vim-multiple-cursors'
    Plug 'airblade/vim-gitgutter'
    Plug 'tfnico/vim-gradle'
    Plug 'ekalinin/dockerfile.vim'
    Plug 'artur-shaik/vim-javacomplete2'
    Plug 'apalmer1377/factorus'
    Plug 'easymotion/vim-easymotion'
call plug#end()


" Plugins configuration
map <C-t> :NERDTreeToggle<CR>
autocmd bufenter * if (winnr("$") == 1 && exists("b:NERDTree") && b:NERDTree.isTabTree()) | q | endif
nnoremap <C-r> :set norelativenumber!<CR>
nmap <CR> o<Esc>
let g:lightline = {
    \ 'colorscheme': 'Dracula',
    \ }
autocmd FileType java setlocal omnifunc=javacomplete#Complete
nnoremap <C-f> :call ToggleFoldingMethod()<CR>
function! ToggleFoldingMethod()
    if &fdm == "indent"
        set fdm=syntax
    else
        set fdm=indent
    endif
endfunction

O que poderia estar errado?