LanguageClient-neovim: syntax highlighting (errors and warnings) doesn't disappear after fixing the errors

• Did you upgrade to latest plugin version? Yes
• Did you upgrade to/compile latest binary? Run shell command bin/languageclient --version to get its version number. Yes. I do run install.sh everytime I upgrade.
• (Neovim users only) Did you check output of :checkhealth LanguageClient? N/A
• Did you check troubleshooting? Yes

Describe the bug

When resolving a syntax error in a file, the error red highlighting is still applied on the line where the bug was and it doesn’t go away. I have to restart Vim in order for the highlighting to be reset.

Here is a minimal example:

https://github.com/sim590/language-client-highlight-bug

Environment

• neovim/vim version (nvim --version or vim --version):

  VIM - Vi IMproved 8.2 (2019 Dec 12, compilé Feb 09 2021 23:51:55)
  

• This plugin version (git rev-parse --short HEAD): a42594c

• This plugin’s binary version (bin/languageclient --version): languageclient 0.1.161

• Minimal vimrc content (A minimal vimrc is the smallest vimrc that could reproduce the issue. Refer to an example here): It is part of the minimal example repository.

• Language server link and version: https://github.com/haskell/haskell-language-server

To Reproduce

Steps to reproduce the behavior:

1. Fetch the minimal example and enter the repository:

   $ git clone https://github.com/sim590/language-client-highlight-bug
   $ cd language-client-highlight-bug
   

2. Open the Main.hs file.

3. Execute the vim normal script: 7Gf=wC undefined^[ where ^[ is the escape key.

Current behavior

The word undefined is highlighted in red even though it is correct syntax.

LanguageClient highlights this region when undefined is being written, so when it sees for instance undef, it correctly highlights the word in red, but as soon as the syntax is correct, i.e. that you write the final d, you can see that the error symbol in the left column is gone, but a subword like undefine is highlighted in red (but not the letter d).

Expected behavior

The highlighting should disappear when an error/warning is fixed.

Screenshots

Additional context

It seems like fixing the warning just above (the line with my_func) does go around the issue. However, you understand that it is not always possible to do so. Sometimes, it doesn’t help either and you have to restart Vim in order to retrieve a usable state.