I've had this problem... it's a fine line between holding it for about 1 sec to open trunk and longer for alarm. I just go open the trunk with my hand now vs using the remote. My wife's 535xiT does the same thing with remote trunk release... pain in the butt.
13 X5 xDrive 35i M-Sport Black/Oyster (Hers)
07 X5 4.8i Sport Black/Black (Winter/DD)
03.5 M3 Cabriolet Steel Grey on Black (Summer Fun)
PAST: 08 E92 M3, 08 535xiT, 06 E90 325i, 87 E30 325i, 85 E30 318i