Watermark is moving left as padding getting higher

[eluser]Unknown[/eluser]
Hello!

I have the code:

Code:

$image_config['source_image'] = './upload/'.$raw_name.'.jpg';
$image_config['wm_text'] = 'balblalblblalblablablalbal';
$image_config['wm_type'] = 'text';
$image_config['wm_font_path'] = './system/fonts/watermark.ttf';
$image_config['wm_font_size'] = '20';
$image_config['wm_font_color'] = '999999';
$image_config['wm_vrt_alignment'] = 'bottom';
$image_config['wm_hor_alignment'] = 'center';
$image_config['wm_padding'] = '0';
$this->load->library('Image_lib');
$this->image_lib->initialize($image_config);
$this->image_lib->watermark();

And there is small problem. I want text to be perfectly centered but it's moved left a little bit. When I increase padding it is moving up as I want, but it is also moving left.

Look on the attachment to see how it looks like. It should be centered, but it's not!

Looks like a bug for me, but I'm not sure.