Hedgemaven mentioned this earlier. But there are good reasons to hold shares both short and long at the same time. For example, I am in that situation now with TPX. I have a 90% gain on my hands, but have only held the stock for 11 months. The difference in tax rates between short and long term cap. gains is 15%. Therefore, if I can hold for another month I get an effective 15% gain, but the stock has to stay at this level! I can buy puts or I can short an equivalent amount of stock to guarantee this. Then if the price goes up or down... it is value neutral. Puts are pretty expensive and depending on the strike price relative to the current stock price, they may or may not do the job or put extra money at risk. So shorting is the way to go.
Don't get me wrong ... I love TPX! Also until the next Q shows us the results of the new plant we may oscillate between 22.50 and 24.50. It may be a great stock for swing trading. Once they can start to brag about the rampup of the new plant... look out above!