problem with post-change trigger

 I am using forms 10g developer version Forms [32 Bit] Version 10.1.2.0.2 (Production) on
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production

In one of my forms, I have used 3 fields named a, b and c.

While running the form, I move the cursor to field a.
In the post-change trigger of this field, I assign some values to fields b and c.

There are post-change triggers written for fields b and c.
The problem is that the post-change triggers of fields b and c are not fired till
the cursor is moved to fields b and c.
I want to execute post-change trigger of fields b and c as soon as I change the value of these fields