Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of electronics and appliance retailer Conn's (NASDAQ:CONN) spiked by 19% shortly after the opening bell Thursday, but dropped throughout the morning to settle in at a strong (but less eye-popping) 9% gain as of this writing. The pop was driven by a double-digit increase in total retail sales in December over the year-ago period.

So what: Conn's reported $132.4 million in total net sales last month, up 11.5% from December 2013. This followed Conn's report of a 19.4% year-over-year gain in net sales for November. Same-store sales declined by half a percentage point in December, but this small drop came a year after Conn's reported monster same-store sales growth of 38.5% for December 2013. The company blamed the decline on a 5% to 7% sales headwind due to tighter underwriting standards, and also noted that same-store sales actually grew by 1.4% when excluding Arizona and New Mexico, where new stores have opened recently.

Conn's reported that 60-plus day delinquencies slipped from 10% in November to 9.7% in December. CEO Theodore Wright also pointed out that shorter-term delinquencies were running "well below" rates seen a year ago.

Now what: Today's pop does little to salve the pain of Conn's shareholders, who have seen the retailer's stock become one of the past year's worst with a decline of over 75%. Conn's delinquency problems are well known and have not yet been fully addressed, but the company appears to be working toward better lending practices, which could help put a floor on its share price and send it back to growth if things go well over the coming quarters.

Conn's P/E is barely in double-digits today, but its free cash flow has not been positive on a trailing 12-month basis since mid-2013 and has yet to show signs of genuine improvement. I'd keep an eye on the stock, but would caution against buy-now optimism over one reasonably solid sales report.