AlphaGolf_fr on "Adding a version number to CSS (and JS) files"

I'd like to append a build number to the CSS and JS file names of my plugin, instead of ?ver=3.8, so that the latest version of the files are sent to the browser with new releases of my plugin.

As per the Codex, I'm using this and it works fine, I do see the build number appended to my filename:
wp_enqueue_script( 'wp-symposium-toolbar', plugins_url( 'js/wp-symposium-toolbar.js', __FILE__ ), array( 'jquery' ), $wpst_buildnr );

But I'm using this and it doesn't work:
wp_enqueue_style( 'wp-symposium-toolbar_admin', $adminStyleUrl, array(), $wpst_buildnr );

Note that these variables are correctly set. Any suggestion why it doesn't work?

Thanks