The discrepancy seems to be in the following files:

in 1.1.6 - wiki_mediawiki_api.php in function wiki_mediawiki_get_url_for_page_id

function wiki_mediawiki_get_url_for_page_id( $p_page_id ) {
    $t_root_url = config_get_global( 'wiki_engine_url' );

    $t_root_namespace = config_get( 'wiki_root_namespace' );

    if ( is_blank( $t_root_namespace ) ) {
        $t_page_id = $p_page_id;
    } else {
        <b>$t_page_id = $t_root_namespace . ':' . $p_page_id;</b>
    }

    return $t_root_url . 'index.php/' . urlencode( $t_page_id );
}

vs. in 1.2.1 - MantisCoreWikiPlugin.class.php in function base_url

function base_url( $p_project_id=null ) {
    $t_base = plugin_config_get( 'engine_url' ) . 'index.php/';
    if ( !is_null( $p_project_id ) && $p_project_id != ALL_PROJECTS ) {
        $t_base .= urlencode( project_get_name( $p_project_id ) ) . ':';
    } else {
        $t_base .= urlencode( plugin_config_get( 'root_namespace' ) );
    }
    return $t_base;
}