mefiu,

I was not able to reproduce your problem with a fresh install of the latest stable version of MantisBT (1.2.15 at the moment).

Please provide detailed, step-by-step instructions to reproduce the issue. Additional information listed below may also be useful:

• Exact version of PHP, Database, Web server and Operating System
• Relevant customizations (e.g. changes in config_inc.php, etc)
• Installed plugins or custom functions ?
• Was the MantisBT source code modified in any way ?

MantisBT Version: 1.2.15
Schema Version: 183
Plugins: http://i.imgur.com/UBZiJmr.png
PHP is: 5.4.4-14 (http://i.imgur.com/AoaAxsp.png)

Only diferrence in sources compared to clear 1.2.15 is config.php:

<?php
$g_hostname = 'localhost';
$g_db_type = 'mysql';
$g_database_name = 'mantis';
$g_db_username = 'root';
$g_db_password = '';

$g_administrator_email  = 'me@somehost';
    $g_webmaster_email      = 'me@somehost';

    $g_from_email           = 'bugtracker@somehost';
    $g_from_name            = 'Mantis';
    $g_email_receive_own    = ON;

    $g_return_path_email    = 'office@somehost';

    $g_allow_file_upload    = ON;
    $g_allow_signup         = OFF;
    $g_default_language     = 'polish';
    $g_phpMailer_method     = PHPMAILER_METHOD_SMTP;
    $g_email_send_using_cronjob = ON;

    $g_logo_image           = 'images/logo.jpg';
    $g_show_queries_count   = OFF;
    $g_status_colors                = array( 'new'                  => '#ffa0a0', # red,
                                             'feedback'             => '#ff50a8', # purple
                                             'acknowledged'         => '#ffd850', # orange
                                             'confirmed'            => '#ffffb0', # yellow
                                             'assigned'             => '#c8c8ff', # blue
                                             'resolved'             => '#99FF99', # buish-green
                                             'closed'               => '#e8e8e8'); # light gray

    $g_reopen_bug_threshold                 = REPORTER;

$g_display_errors = array(E_ERROR => 'inline');

    $g_show_detailed_errors = ON;

?>

Don't set $g_display_errors
Does this fix your issue?

Works like a charm!
Thanks :)

Still wondering though if this error-tracing feature should result in such a confusing behaviour...
We've experienced quite a few emails being sent today morning to not-expecting users with a blank issue, assigned to root-top project tree.
Maybe our user just jumped to not-existing issue and added a note... I still don't know...

Have a look at file config_defaults_inc.php for a description of $g_display_errors
You should never change this setting for production environment.
You may change the setting for development purposes, but change it the way it's documented.