unfortunately the suggested fix seems to fail in version 1.1.0
it results in status change mails no longer being sent at all?

using $t_status2 instead of $t2_status in suggested fix works like without using fix (no advantage for the status names containing spaces but the others getting sent)

The design is not to ever have spaces in the status names. For example, if you want to define status "Awaiting Test" with id 60, then you should define it as follows:

In the $g_ enum, you use "60:awaitingtest".
In the $s string, you use "60:Awaiting Test".

Anywhere in the configuration, you use the "awaiting_test" name, rather than the localized name which has the capitalization and the spaces.

confirmed: I have obeyed this rule, nevertheless I've had the "send mail on status change" box in user's configuration not set. There are several settings above for "send mail on 'confirmed'", "...'reopened'" and so on, so this was why only SOME status changes have been sent by mail (unfortunately those were the ones with spaces in their s_string variable - which is really irrelevant).

Thanks. Following Victor's design rule works as expected without code changes.

It would be useful if the documentation reflected that. The example given in http://www.mantisbt.org/manual/manual.customizing.mantis.customizing.status.values.php
uses "to be tested" (with spaces not underscores).

This works for me too! Why not closing this issue, i had to click through all related tickets to find this one. All related bugs in the original were marked as new and related.