REDOLOG divide in two lines large VARCHAR

Hello,

I'm making a PL/SQL redo log analyzer. When I use LogMiner to analyze a table that contains a large varchar, the redo log divide my INSERT in that table in one INSERT + one UPDATE. Let's see a sample:

I execute these SQL lines:

CREATE TABLE DUMMY (ID NUMBER, VARCHAR_LARGE VARVHAR2(32767));

INSERT INTO DUMMY (ID) VALUES ('1');

commit;

Then I execute LogMiner to view the SQL lines executed and the result is:

INSERT INTO DUMMY (ID, VARCHAR_LARGE) VALUES ('1', 'LM_EMPTY_STRING');

UPDATE DUMMY SET VARCHAR_LARGE=NULL WHERE ID='1';

What is the reason to split in two lines when I just execute an INSERT?