styles are lost when modify bundle output using postcss

Inside my project i have a index.css with the following content:

/* src/css/index.css */

@import "global/reset.css";
@import "global/variables.css";
@import "global/utilities.css";

to use my @import rules, i modify the bundle output with postcss like this:

const bundlerPlugin = require("@11ty/eleventy-plugin-bundle");
const postcss = require('postcss')
const postcssrc = require('postcss-load-config')

const ctx = { env: process.env.ELEVENTY_ENV }

module.exports = (config) => {
 config.addPlugin(bundlerPlugin, {
   transforms: [
     async function(content) {
       if (this.type === 'css') {
         const { plugins } = await postcssrc(ctx)
         const { css } = await postcss(plugins).process(content, { from: this.page.inputPath, to: null });
         return css;
       }
       return content;
     }
   ]
  })
}

my postcss.config.js looks like this:

const postcssImport = require('postcss-import')
const postcssNested = require('postcss-nested')
const autoprefixer = require('autoprefixer')
const cssnano = require('cssnano')

module.exports = (ctx) => ({
  plugins: [
    postcssImport({
      path: ['./src/css'] // to resolve all css files in src/css/global/*.css
    }),
    postcssNested,
    autoprefixer,
    ctx.env === 'production' ? cssnano : undefined
  ]
})

i added the index.css file to my base.webc layout like this:

<!-- layouts/base.webc -->
<link webc:bucket="global" rel="stylesheet" href="../css/index.css">
<style webc:if="this.eleventy.env.runMode === 'serve'" webc:keep @raw="getBundle('css', 'global')"></style>

at this point, all works, all css files will be merged together, but...

when i add my navbar component styles to the global bucket like this:

<!-- components/site/site-nav.webc -->
<style webc:bucket="global">
  /* my navbar styles */
</style>

all my styles inside my index.css are lost, only my site-nav.webc styles are in the bundle output

why this happen? is this is a bug?

Reproduce the setup using the transform in the issue, postcss.config.js, layouts/base.webc, and components/site/site-nav.webc. Inspect how the global bucket is assembled and how the PostCSS transform receives its content. Done means identifying why adding the component style changes the bundle and documenting or correcting the behavior with a regression test.