i can present method to setup mantisbt 1.2 on MSSQL 2008
there is a small hit:
when we installing mantisBT we must use $g_db_type = 'odbc_mssql'
when we using mantisBT we must switch to $g_db_type ='mssqlnative'
the same thing with $g_hostname = 'Driver={SQL Server};SERVER=(local)\old;DATABASE=mantis;UID=mantisdb;PWD=123;'; (for ODBC)
$g_hostname ='(local)\old';(for MSSQL)

and dont forget you cant install ver 1.3 on MS SQL 2000.

wihtout patches 1.3.0. rc1
at https://www.mantisbt.org/forums/viewtopic.php?f=4&t=21339&start=30#p58621
you cant install this on MS SQL >=2005.

Because ADOdb provider is broken.

ADOdb included with 1.3.0 rc1 has no support for MS SQL.
its simple absent.
and on picture we see executing not modified T-SQL for MS SQL .
this SQL must be sliced to three SQL statements.
read this for details.
https://www.mantisbt.org/forums/viewtopic.php?f=4&t=21339&start=15#p58602

but 1.2.0 ADOdb provider has full support for MS SQL.
the diff is 1.3.0 has resetted php files for MS SQL code.

there is some commit about this
https://github.com/mantisbt/mantisbt/commit/19dbfb0e290a30fcfe1ec29566e611d36c1c7aa9

this commit adds this resetted code for MS SQL.

Following the suggestion on the first note, I tried to do a clean installation using 1.2.19 with SQL Server 2012 but without success.

I set my configuration in config_inc.php as:
$g_hostname = 'Driver={SQL Server Native Client 11.0};SERVER=localhost;DATABASE=bugtracker1219;UID=mantis;PWD=mantis;';
$g_db_type = 'odbc_mssql';

The installation crashes on:
BAD
ALTER TABLE mantis_user_pref_table ALTER COLUMN redirect_delay INT DEFAULT 0 NOT NULL
[Microsoft][SQL Server Native Client 11.0][SQL Server]Incorrect syntax near the keyword 'DEFAULT'.

not Driver={SQL Server Native Client 11.0}
must be $g_db_type ='odbc_mssql'

and Driver={SQL Server}

Fixed by 0022063