Indeed, I guessed it has something to do with the theme. Mine uses a regular "page" as a home.
It seems a bit tough to fix this with Wordpress SEO by Yoast (when I don't have the problem with All in one SEO). Maybe, if I may, it could be something to fix for the next version.
My title code is pretty long, I have no idea what to replace, may I ask for a little more help ?
It's like that :
<title>
<?php
$prefix = false;
if (function_exists('is_tag') && is_tag()) {
single_tag_title('Tag Archive for "');
echo '" - ';
$prefix = true;
} elseif (is_archive()) {
wp_title(''); echo ' '.__('Archive',EWF_SETUP_THEME_DOMAIN).' - ';
$prefix = true;
} elseif (is_search()) {
echo __('Search for', EWF_SETUP_THEME_DOMAIN).' "'.wp_specialchars($s).'" - ';
$prefix = true;
} elseif (!(is_404()) && (is_single()) || (is_page())) {
wp_title(' ');
echo '';
} elseif (is_404()) {
echo __('Not Found', EWF_SETUP_THEME_DOMAIN).' - ';
}
if (is_home()) {
bloginfo('name'); echo ' - '; bloginfo('description');
} else {
bloginfo('name');
}
if ($paged > 1) {
echo ' - page '. $paged;
}
?>
</title>