AFTER PORPOISING OF THE ACFT WHILE ON FINAL APCH A B737 PIC FILES A RPT ON THE VIOLATION OF THE ILS HOLD SHORT AREA FOR RWY 26L.

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ACFT WAS CLRED FOR ILS 26L APCH IN IMC. AUTOPLT ON; ESTABLISHED ON THE LOC/GS; AND CLRED TO LAND. GS SUDDENLY JUMPED UP AND THEN DOWN ABOUT 1/2 DOT WITH THE AUTOPLT STAYING CONNECTED. THE OSCILLATIONS WERE SUCH AS TO ALARM THE CREW. I REPORTED THE PROB TO THE TWR BEFORE LNDG AND THEY INDICATED THE PROB MIGHT BE DUE TO XING ACFT ON THE APCH END OF 26L. AFTER LNDG I CALLED THE TWR TO FURTHER EXPLAIN THE AUTOPLT UPSET AND THE IMPACT ON PAX. I NOTED TO THEM THERE WAS AN ACFT STOPPED INSIDE THE ILS PROTECTED AREA WHEN WE FLEW OVER THE APCH END OF THE RWY; AND THAT THERE WERE ALSO SEVERAL ACFT SEEN XING THE APCH END OF THE RWY; WHEN WE WERE ON SHORT FINAL AFTER BREAKING OUT OF THE CLOUDS. THE TWR CTLR I SPOKE WITH INDICATED HE HAD NO IDEA WHICH ACFT WERE ON ILS APCHS AND WHICH WERE ON VISUAL APCHS DURING THE TIME OF THE OCCURRENCE. THIS SIT NEEDS ATTN SINCE WE ARE ONLY IN THE FIRST MONTH OF OP WITH RWY 26L AFTER CONSTRUCTION. WHEN ACFT ARE CLRED FOR AN ILS IN IMC CONDITIONS; THE ILS PROTECTED AREA SHOULD BE JUST THAT; PROTECTED. AT THE VERY LEAST AIRCREWS SHOULD BE NOTIFIED OF ANY ENCROACHMENT OF ACFT WHICH MAY AFFECT THE PERFORMANCE OF THE ILS SYS.