Wrong t() placeholder for $user->name

The placeholder used in the call to t() made in drupalmu_helper_preprocess_page() should be %name, or @name.
This is because the !name placeholder puts the $user->name value without to filter it out for character which would cause some problems in HTML content.

See the documentation, where in an example is used code like $message = t('%name-from sent %name-to an e-mail.', array('%name-from' => $user->name, '%name-to' => $account->name));.