xnoremap S <Plug>VgSurround gets overridden

[mawkler]

xmap for <Plug>VgSurround seems to get overridden by <Plug>VSurround. For some reason this seems to only happen in Neovim, because when I do the same thing in Vim I get the expected behaviour.

To reproduce:

1. Use the following init.vim

   call plug#begin('~/.vim/bundle')
   Plug 'tpope/vim-surround'
   call plug#end()
   
   xnoremap S <Plug>VgSurround

2. Launch Neovim

3. :xmap S outputs x S <Plug>VSurround (note that it's not VgSurround as expected)

4. Using the same config for Vim and doing :xmap S outputs x S * <Plug>VgSurround.

I can xmap other commands than S to <Plug>VgSurround fine, so it seems that it is S specifically that is getting overridden.