Hover window disables syntax highlight.

[vext01]

Describe the bug

Hovering window produced by K binding disables syntax highlighting.

Environment

• neovim/vim version (nvim --version or vim --version): NVIM v0.5.0-622-gf26df8bb6
• This plugin version (git rev-parse --short HEAD): 0e5c954
• This plugin's binary version (bin/languageclient --version): languageclient 0.1.158
• Language server link and version: rust-analyzer af6e9a7eb
• OS: Debian 10 amd64

To Reproduce

Steps to reproduce the behavior:

• Install rust-analyzer into $PATH.
• Use the following minimal config:

if empty(glob('~/.vim/autoload/plug.vim'))
    silent !curl -fLo ~/.vim/autoload/plug.vim --create-dirs
                \ https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
    autocmd VimEnter * PlugInstall | source $MYVIMRC
endif

syntax on

call plug#begin('~/.vim/plugged')
Plug 'autozimu/LanguageClient-neovim', {
    \ 'branch': 'next',
    \ 'do': 'bash install.sh',
    \ }
call plug#end()

set hidden
if executable('rust-analyzer')
    let g:LanguageClient_serverCommands = {
            \ 'rust': ['rust-analyzer'],
    \ }
endif

nmap <silent>K <Plug>(lcn-hover)

• Install plugins and update remote plugins.
• cargo new --bin myprog
• nvim -u </path/to/config> src/main.rs
• Position cursor over the main symbol. Press K.

Hover window appears, text in the buffer behind is no longer syntax highlighted(!).

Screenshots

Can anyone repro, or just me?

FWIW, I had the same issue with hovering windows using vim-lsp.

[vext01]

This turned out to be due to a syntax off in ~/.vim/ftplugin/markdown.vim.