Yii2 AssetBundle convert less file but don't publish - yii2

Question

I have a widget where I wanted to convert a less file to an css file.
The conversion works perfectly. But now I want that the less files aren't published to the web/assets directory.
And here the Pain begins...
This is my code:
class BreadcrumbsAsset extends \yii\web\AssetBundle
{
public $css = [
'css/breadcrumbs.less',
];
public $js = [
'js/breadcrumbs.js',
];
public $depends = [
'yii\web\YiiAsset',
'yii\bootstrap\BootstrapAsset',
];
public $publishOptions = [
"only" => [
"css/*",
"js/*",
],
'except' => [
"doc/",
"*.less",
],
];
}
But with the except setting set the css file isn't generated.
Also when I try the other way around and set:
public $publishOptions = [
"only" => [
"css/*.css",
],
The css file isn't generated from the less file any more.
So how does this supose to work?
When the to options only and except are added for this this case:
https://github.com/yiisoft/yii2/issues/2511 (AssetBundle should not publish .less or .coffee files)
https://github.com/yiisoft/yii2/issues/8566 (AssetManager support for choosing file/dir to be publish)
The Publishoptions are descriped like this:
only: array, list of patterns that the file paths should match if they want to be copied.
except: array, list of patterns that the files or directories should match if they want to be excluded from being copied.
And in the Filehelper which is used for the File Publish the except and only are descriped like this (from the Yii2 Filehelper Source):
- `except`: array, list of patterns excluding from the results matching file or directory paths.
Patterns ending with slash ('/') apply to directory paths only, and patterns not ending with '/'
apply to file paths only. For example, '/a/b' matches all file paths ending with '/a/b';
and `.svn/` matches directory paths ending with `.svn`.
If the pattern does not contain a slash (`/`), it is treated as a shell glob pattern
and checked for a match against the pathname relative to `$dir`.
Otherwise, the pattern is treated as a shell glob suitable for consumption by `fnmatch(3)`
`with the `FNM_PATHNAME` flag: wildcards in the pattern will not match a `/` in the pathname.
For example, `views/*.php` matches `views/index.php` but not `views/controller/index.php`.
A leading slash matches the beginning of the pathname. For example, `/*.php` matches `index.php` but not `views/start/index.php`.
An optional prefix `!` which negates the pattern; any matching file excluded by a previous pattern will become included again.
If a negated pattern matches, this will override lower precedence patterns sources. Put a backslash (`\`) in front of the first `!`
for patterns that begin with a literal `!`, for example, `\!important!.txt`.
Note, the '/' characters in a pattern matches both '/' and '\' in the paths.
- `only`: array, list of patterns that the file paths should match if they are to be returned. Directory paths
are not checked against them. Same pattern matching rules as in the `except` option are used.
If a file path matches a pattern in both `only` and `except`, it will NOT be returned.
So how should this only and except settings work?
Or is this a Bug?
Forgot to mention that of course I have the newest yii2 version installed (the only and except settings for publishOptions were introduced with yii 2.0.6)