Hi folks, I'm seeing that my custom.ccs is not loaded even if the file exists.
If I change
this:

// CUSTOM CSS

if (is_file(T3_TEMPLATE_PATH . '/css/custom.css')) {

	$this->addStyleSheet(T3_TEMPLATE_URL . '/css/custom.css');

}

to this

// CUSTOM CSS

//if (is_file(T3_TEMPLATE_PATH . '/css/custom.css')) {

	$this->addStyleSheet(T3_TEMPLATE_URL . '/css/custom.css');

//}

Note: The if returns false...
The file is loaded, but isn't a good practice...
I don't know how to solve this without checking if the file is correct. I've created the file multiple times and on different folders:
templates/t3_bs3_blank/local/css/themes/mytheme/custom.css
templates/t3_bs3_blank/css/custom.css
templates/t3_bs3_blank/local/css/custom.css

But without results. This is important for me since I do the final touches through developer tools.
I used T3 several times but this is the first time I have this issue. And I always work with the local folder since I know that my files might be overwritten, and helps me keep everything clean.

Thank you in advance, for now I'm using the commented solution, but I want to know what I'm doing wrong, or if this is a bug.

Regards
Florencia