C++Builder 5, IBO 3.6C, IB 6.01

Please listen to that trouble about triggers in IBO.
I have a TABLE with a TRIGGER BEFORE INSERT. Within my
IBO-CppBuilder application, the trigger don't fires!
Let me explain: the trigger contains some like this

CREATE TRIGGER mytableTrigBI FOR MYTABLE
BEFORE INSERT AS
BEGIN

MYTABLE.SOMEFIELD='Some text';

END

If I insert one record using IB Console, SOMEFIELD takes correctly the
text I assign in the trigger. But with the app, where the table is
handled with a TIB_Query, I suspect the trigger don't fires because
nothing is assigned to SOMEFIELD.
Is this possible?
Which property can cause this behaviour?
TIA
Hugo.