BUG #5577: Boolean operation should not be Complete boolean evaluation

The following bug has been logged online:

Bug reference:      5577
Logged by:          y.y.chen
Email address:      yychen@mail.clhs.tyc.edu.tw
PostgreSQL version: 8.4.x
Operating system:   WINDOWS-XP
Description:        Boolean operation should not  be Complete boolean
evaluation
Details:

It's happen in version 8.3.11,8.4.1,8.4.4
but not in 9.0.0.beta3.

When I run in PlpgSQL /Trigger :

IF ( TG_OP = 'INSERT') OR (old.size<>new.size) then
........
END IF;

While TG_OP is 'INSERT' and then raise a exception
 RECORD old never be defined !

It's not an efficiency SQL-scripts for "Complete boolean evaluation "!