AN A320 ACFT WITH XING RESTR CLRNC; RPTR CAPT ENTERED RESTR IN FMC AND OBSERVED ACFT ON PROFILE WHILE OBTAINING ATIS. WHEN RPTR ENTERED NEW RWY IN FMC THE RESTR DROPPED OUT AND RPTR WASN'T ABLE TO MAKE IT. HE FAULTS THE ACFT SYS BECAUSE IT DOESN'T PROVIDE A WARNING WHEN RESTRS ARE DROPPED OUT.

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I AM RPTING AN UNSAFE CONDITION IN THE AIRBUS FMC SOFTWARE. DURING MY DSCNT I WAS ASSIGNED A XING ALT. I HAD A WIND OF 130 KIAS RIGHT ON MY TAIL; MAKING A MENTAL COMPUTATION OF THE PROFILE DIFFICULT. I PROGRAMMED THE ALT IN THE FMC WHICH CORRECTLY COMPUTED THE DSCNT PROFILE AND THE ACFT WAS ESTABLISHED ON THE PROFILE. UPON RECEIVING ATIS I NOTED A RWY CHANGE. I INSTALLED THE RWY CHANGE. AT THAT MOMENT THE FIRST FLT ATTENDANT ENTERED THE COCKPIT WITH A BRIEF DESCRIPTION OF A PROB OCCURRING IN THE CABIN. UNKNOWN TO ME; THE FMC HAD REMOVED THE XING RESTR AND RECOMPUTED THE PROFILE AND CONTINUED THE DSCNT IN VNAV WITHOUT THE RESTR AND WITHOUT WARNING. UPON DISCOVERING THIS; I INFORMED THE CTLR THAT IT WOULD BE IMPOSSIBLE TO MEET THE RESTR. HE SAID; 'NO PROB; THERE WAS NO TFC.' I LATER DISCOVERED THIS IS NOT A MALFUNCTION BUT THE NORMAL WAY THE AIRBUS IS PROGRAMMED. EVERY TIME THE RWY IS CHANGED EVEN IF IT DOES NOT AFFECT THE ARR; ALL PLT ENTERED RESTRS ARE REMOVED AND THE PLTS ARE NOT MADE AWARE OF THE CHANGES. THIS IS UNSAFE. THE COMPUTER SHOULD NOT REMOVE PLT ENTERED RESTRS. THIS TAKES 'MGMNT BY EXCEPTION' TO A HIGHER LEVEL.