Why in the world are insiders still selling Mandalay Resort Group (NYSE:MBG)? OK, its casino operations are a bit rough around the edges, but Mandalay just keeps getting hotter where it counts -- the Las Vegas Strip.

In the just-reported fourth quarter, operating cash flow from Strip properties surged 25% over last year, driven by an impressive 22% increase in revenue per available room (REVPAR) at its hotels. REVPAR at the flagship Mandalay Bay alone rose 26%, with the average room topping an astounding $192 per night.

Riding that strength, overall fourth-quarter revenue climbed 10% to $604.1 million, while operating cash flow jumped 14% to $136.7 million. At the same time, net income clocked in at $22.8 million, or $0.35 per share.

All was not perfect, however. Operating cash flow at the 50%-owned Grand Victoria in the Chicagoland market fell 41% to $24.7 million due to brutal Illinois tax rates -- the same 70% top tax rate that put the hurt on Harrah's (NYSE:HET), Argosy (NYSE:AGY), and Penn National (NASDAQ:PENN). Mandalay's Nevada properties outside of Las Vegas also saw a slight decline in operating cash flows, reflecting growth in Native American gaming in California.

That noted, given the explosion in Las Vegas, it isn't surprising that Mandalay shares more than doubled over the past year. However, Mandalay's exceptional business and stock performance has gone in tandem with persistent insider selling.

Several months ago, we noted that Mandalay's top execs -- Chairman Michael Ensign and Vice Chairman Bill Richardson -- soldall of their shares in a blinding flurry. Now, you'd think they'd stop selling when they ran out of shares to sell, but hey, that's what options are for! That's right, the activity picked up again in January.

So yes, Las Vegas is hot, and there's no question that Mandalay is a premium operator. All the same, I just can't think of a compelling reason to own a stock that no one at the top wants to. As it is, Mandalay shares look richly valued, which should make this one pretty easy to avoid. Just follow the insiders.

Give us your take on the Mandalay Resort Group discussion board - only at Fool.com. Jeff Hwang owns none of the aforementioned companies.