Investors wanted more meat on the bone from Costco Wholesale (COST) .

The warehouse king used its notorious cut-rate pricing on bulk food and surprising selection of higher end items to post an 8.4% same-store sales increase for the holiday season quarter. Earnings smashed through analyst estimates for the quarter ended Feb. 18, coming in at $1.59 a share vs. the $1.47 a share expected.

Even still, Wall Street sent Costco shares slightly lower on Thursday likely for several reasons.

First, what looked like a massive earnings beat was actually an earnings miss as the results included a 17 cent a share lift from the new tax reform plan. Further, like other retailers such as Target (TGT) and Walmart (WMT) that battled Action Alerts Plus holding Amazon (AMZN) online during the holidays, gross profit margins compressed. Costco's gross profit margin fell slightly from the prior year to 10.98%. 

With inflation starting to pickup, and margins already under pressure, Costco bulls could be wondering if it's time to ring the register. Before today's release, Costco's stock had risen 12% over the past year.