It's thriving right now, but the market didn't like its fourth-quarter report.Costco Wholesale (COST -2.92%) is known for being a perpetual market beater, but Costco stock is actually lagging the market this year, up only 3% while the S&P 500 is up 13%. The market gave the company's latest results a mediocre reception despite coming in ahead of forecasts for both sales and earnings and management giving an upbeat feeling about the future.Has Costco's sheen finally worn off? Here are five things you need to ...