SPLIT PERSONALITY OF KARNA (ii PART)

Sri Mdhwacharya  clarifies this point thus: 

When Kunti wanted to test the power of Mantras that Rudramshasambhoota Durvas had taught her, she first recited the Mantra to invoke and propitiate Sun God. She took bath during her periods and invoked the Sun casually. The Shloka in this regard is:

Rutau tu sA samAplutA pareekShaNAya tanmanOho|

SamAhwayad DivAkaram sa chAjagAm tatkShaNAt||

After she invoked the Sun, he appeared in front of her and she could not send him away without sensuously satisfying him. 

Sa tatra jajnivAn swayam dwiteeyarUpakO viBhuhu|
SavarmadivyakunDalO jwalanniva swatEjasA(Mahabharata Nirnaya- Canto 11 Shloka 155)||
Adorned with divine Kundalas and sparkling with his natural rdiation, Sun entered Kunti in his alternate form. The real clarification is this:
PurA sa VAlimAraNapraBhUtadOShakANAt|
SahasravarmanAminAsrENa vEShTitO(a)jani||

Earlier (during Tretayuga), since he (Sun) had prompted Srirama as Sugreeva to kill Vali (Indramsha), he (Sugreeva or Sun) had attracted a sin. Therefore, he (Sun) was born in Kunti with the traits of a demon called Sahasravarma.
TaThApi RAmasEvanAddarEshcha sanniDhAnayuk|
SudarshaneeyakarNataha sa KarNanAmakO(a)Bhavat||

However, since the Sun had greatly served and revered (as Sugreeva) Srirama, he had the good fortune of being very close to the Lord. Since he had very beautiful ears, he came to be called as Karna. 

Whenever his mind was being afflicted by the traits of Sahasravarma (demon), Karna used to be uncultured, uncivic, amoral, unjust and cunning.