A set of misprinted U.S. postage stamps has increased in value after reports that some CIA employees tried to sell them. John Reznikoff has acquired 18 of 85 available stamps for nearly $1 million. "You have to understand the mentality of a stamp collector," said Reznikoff, founder of the University Stamp Company Inc. here. "They're going to show the stamp to their grandchildren and say, 'That's Stampscam.' " Reznikoff paid about $50,000 each for the $1 stamps depicting an inverted candlestick. The stamps were from a batch of 95 that a CIA employee bought for the agency in March, 1986, at a McLean, Va., post office.