Laravel 4 CSS file validation failing - php

Question

I have an upload form that has validation checks whether an item is a valid CSS file or not. I do try to upload a .css file but the validation fails.
Here's the bit where I try to validate the code on my controller:
private function _queueArticle($ref = NULL)
{
$input = Input::all();
$vrules = Config::get('validation.queue_article');
//validate inputs
$validation = Validator::make($input, $vrules);
if ( $validation->fails() ) {
return ( $ref === NULL ) ?
Redirect::to($redir_path)->withErrors($validation)->withInput() :
Redirect::to($redir_path)->withErrors($validation);
}
}
Here's what's $vrules:
'queue_article' => array(
'title' => 'required|max:255',
'body' => 'required',
'slug' => 'unique:articles,slug',
'hero' => 'required|image',
'custom_css' => 'mimes:css'
)
I believe it's failing because it's using PHP's finfo, which is known to fail detecting css not as text/css, but rather text/plain. Doesn't Symfony, Laravel's 'companion code' here (don't know the term), has its own validation class that successfully clears CSS for what it is?
More importantly, what can I do about this?
UPDATE: Error message shows my custom error 'Please upload a valid CSS file.' From app/lang/en/validation.php:
'custom' => array(
'password_old' => array( 'required' => 'Please enter your current password.' ),
'password' => array( 'confirmed' => 'The new passwords don\'t match.' ),
'hero' => array(
'required' => 'A header image is required.',
'image' => 'The header file you included is not valid. Please upload a valid image.'
),
'custom_css' => array('mimes' => 'Please upload a valid CSS file.')
)
UPDATE 2: I checked var_dump($validation) and showed zero contents on array messages and failedRules. It also shows the CSS file having mime type as text/css. All is well, eh, except when I var_dump($validation->fails()) it returns a bool of true.
Additional info will be provided upon request.
Thanks!