That would explain why I'm suddenly getting all these new ticket emails from this Mantis installation.

I have a similar issue: I do NOT get E-Mail when changing status to anthing else but 'new' or 'resolved' though it is set to send E-Mail in any event.

(The e-mail even is NOT send when adding a note while changing the status - so the fact that I've added a note seems to be ignored when I do it while changing the status - maybe that's by design?)

Confirmed on this bug tracker. Thanks for the bug report.

I've got more detailed information now:
I get an E-Mail for new, feedback, resolved, closed

I do NOT get an E-Mail for assigned (which I have overwritten by my_assigned).
And I do NOT get an E-Mail for 3 additional self-definted status and
I do NOT get an E-Mail for 'confirmed'.

The last is what lead me to a possible reason: On the manage users page the line "E-Mail on confirmed" is missing (like all lines for self-defined status).

It seems that this has to be added to
core/user_pref_api.php
account_prefs_inc.php
account_prefs_update.php
admin/schema.php
config_defaults.php or rather custom_config.php

Is there an easier way to get E-Mail notification for customized status?

OK email_on_new should now be fixed in 1.2.x and 1.3.x (master).

Please note that the email preferences you see are not meant to match the actual statuses you're using in your Mantis installation. "Resolved" as seen in the email preferences doesn't refer to the "resolved" status but rather, it refers to the concept of a bug being considered fixed/resolved. For instance, you may have a custom workflow configured where a bug is only considered resolved once it reaches the "tested" status.

The notification system is in desperate need of an overhaul (which I haven't done in fixing this bug). I've tried to apply some interim fixes for 1.2.x to at least gain some sanity before hopefully an overhaul of how we handle notifications.