Grunt `purgecss` doesn't execute on all files when more than two.

[kiril-daskalov]

Describe the bug
Grunt purgecss doesn't execute on all files when more than two.
I have 4 files and each time purge css is started the output is different. Sometimes output all files some times 3, sometimes 2.

To Reproduce
Use this simple configuration.

config.purgecss = {
  my_target: {
    files: {
      "main.css": "main.css",
      "calculator.css": "calculator.css",
      "media.css": "media.css",
      "text.css": "text.css",
    },
  },
};

Expected behavior
Should execute on all files all times.

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• OS: Bug Sur and Linux Mint
• Package
  "grunt-purgecss": "^4.0.2",
  Node: v14.15.0
• Version 4.02

Additional context

[z3niths]

I confirm this's happening to me too
In my case, it's slightly different. I had multiple sources process into one destination.

"files": {
      "static/dist/destfile.css": [
        "file1.css",
        "file2.css",
      ],
    }

• Mac M1
• Node v14.15.3
• "grunt": "^1.4.0",
• "grunt-purgecss": "^4.0.3",

Additional syntax

"files": [
      {
        src:
          [file1.css', 'file2.css'],
        dest: "static/dist/destfile.css"
      }
    ]

This syntax also doesn't work using src/dest

It's always process first file (file1.css)