Costco (COST) just put up one of the cleanest quarters in retail, but the stock fell anyway.

The retail giant set fresh records at the gas pump, leaned on a fast-growing online business, and kept members renewing at rates most retailers can only envy.

Yet shares slid in the days after the report, and that gap between the results and the reaction is the real story for anyone holding COST or weighing a buy.

Costco’s record quarter met a market focused on valuation

The numbers were strong almost everywhere you looked.

Net sales rose 11.6% to $69.15 billion, and total revenue of $70.53 billion came in ahead of Wall Street’s estimate, CNBC reports.

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So, what went wrong?

Adjusted earnings…