FLT CREW OF B733 CROSSED HOLD LINE OF RWY 19L AT SNA WITHOUT CLRNC. SMA ON FINAL APCH WENT AROUND AS A RESULT.

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SNA HAS PARALLEL RWYS 19R AND 19L IN USE. WE WERE TAXIING FOR TKOF. GND CTL HAD CLRED US TO HOLD SHORT OF TXWY L NEAR THE DEP END AND CONTACT THE TWR. TWR CLRED US TO 'TURN L ON TXWY L' AND HOLD SHORT OF RWY 19L; ACR'S USE RWY 19R. NORMALLY; WHEN TWR CLRS YOU TO 'TURN L ON TXWY L' YOU ARE CLRED TO CROSS RWY 19L AND HOLD SHORT OF RWY 19R. NOT THIS TIME. WE WERE CLRLY TOLD TO HOLD SHORT OF RWY 19L. I EVEN REPEATED THE CLRNC TO THE FO. AFTER TURNING L ON TXWY L I THEN; OUT OF HABIT; CROSSED THE RWY 19L HOLD LINE AND WOULD HAVE CROSSED ONTO THE RWY EXCEPT I SAW A SMALL PLANE ON SHORT FINAL FOR RWY 19L. I IMMEDIATELY STOPPED SHORT OF THE RWY BUT PAST THE HOLD LINE; AND INSTRUCTED THE FO TO RADIO THAT WE HAD CROSSED THE LINE. TWR ANSWERED BACK THAT THE SMALL PLANE WAS GOING AROUND ANYWAY AND FOR US TO CONTINUE ACROSS RWY 19L AND CLRED FOR TKOF ON RWY 19R. I DID THAT AND NOTHING MORE WAS SAID. THE POINT IS; I DISTINCTLY HEARD THE CLRNC TO HOLD SHORT OF RWY 19L; EVEN REPEATED IT; BUT STILL; OUT OF HABIT; INTENDED TO CROSS RWY 19L AND HOLD SHORT OF RWY 19R AS USUAL. UNTIL NOW I THOUGHT RWY INCURSIONS WERE THE RESULTS OF NOT PAYING ATTN (I'VE NEVER DONE THIS IN 30+ YRS OF FLYING). NOW; EVEN I CAN'T EXPLAIN WHY I DID THIS.