Upgrading a database from SQL Server 2005 to 2012 uncovered a syntax error

I recently upgraded from SQL Server 2005 to 2012. During validation however, a bug was discovered.

A certain trigger was coded as follows:

CREATE TRIGGER [dbo].[trigger] on [dbo].[foo]
FOR UPDATE, UPDATE
AS
    UPDATE foobar
    SET datetime = GetDate()
    FROM bar
    WHERE foobar.id = bar.id
GO

I can safely execute this (oddly) on SQL Server 2005.

However on SQL Server 2012 it throws (what I would expect) a syntax error.

Syntax error: Duplicate specification of the action "UPDATE" in the trigger declaration.

Why does this not throw a syntax error on SQL Server 2005? My google-fu on this has failed me.

Why does this seemingly work on SQL Server 2005?