ANALYSIS:
=========
Zero date(0000-00-00 00:00:00) is generated by the
'BEFORE INSERT' trigger defined on a table with TIMESTAMP
or DATETIME field having the default as CURRENT_TIMESTAMP
or NOW().

Similar behavior is observed with LOAD INFILE queries and
also with BEFORE UPDATE triggers.

Whenever a 'BEFORE INSERT' trigger is defined on a table
and an insert happens on it, the trigger body is executed
first and then the new record is written into the table.
If the trigger body tries to utilize the default values
of the fields in the table, the values used will be
incorrect.

Brief working of 'AFTER INSERT' triggers:
1. Set function defaults for the table.
2. Write record into the table.
3. Process the trigger defined on it.
  3.1 Execute the trigger body.

Brief working of 'BEFORE INSERT' triggers:
1. Process triggers defined on the table.
  1.1 Execute the trigger body.
2. Set function defaults for the table.
3. Write record into the table.

Hence when a 'BEFORE INSERT' trigger is defined for a
table, the evaluation of default functions is not done for
the table before processing the trigger. Thus the default
values of the table are not updated and if the trigger body
tries to utilize these values, incorrect result will be
obtained.

FIX:
====
We are now evaluating the function defaults for a table
before processing the 'BEFORE INSERT' or 'BEFORE UPDATE'
triggers defined on it.