PHP Syntax highlighting in preview window doesn't work when using Treesitter

[benalf]

Using a bare-bones setup. As soon as PHP treesitter parser is installed, syntax highlighting goes blank in the preview window.

It's seems to be related to the janky language design requiring <? opening tag at the start of the file. If the preview window includes the tag, highlighting works fine. Other languages don't have this problem.

Minimal config for reproduction:

local fn = vim.fn

local install_path = fn.stdpath("data") .. "/site/pack/packer/start/packer.nvim"
if fn.empty(fn.glob(install_path)) > 0 then
  PACKER_BOOTSTRAP = fn.system({
    "git",
    "clone",
    "--depth",
    "1",
    "https://github.com/wbthomason/packer.nvim",
    install_path,
  })
  vim.cmd([[packadd packer.nvim]])
end

require('packer').startup(function(use)
  use({
    'williamboman/nvim-lsp-installer',
    config = function()
      require('nvim-lsp-installer').setup({})
    end,
  })
  use({
    "nvim-treesitter/nvim-treesitter",
    run = ':TSUpdate',
    config = function()
      require("nvim-treesitter.configs").setup({
       	-- ensure_installed = {"php"},
      })
    end
  })
  use ({
    "williamboman/mason.nvim",
    config = function ()
      require("mason").setup({})
    end
  })
  use({
      'ray-x/navigator.lua',
      requires = {
          { 'ray-x/guihua.lua', run = 'cd lua/fzy && make' },
          { 'neovim/nvim-lspconfig' },
      },
      config = function()
        require'navigator'.setup({});
      end
  })
end)

require('packer').sync()

vim.cmd [[
  colorscheme murphy
  set background=dark
]]