or maybe this is why - from everyone's favorite site, pvnotes.com
ParkerVision Repeated Short Recalls Over the past few years (at a mininum, 2006 and 2007), there have been repeated short recalls. They are sizeable and appear to be organized. Some large holders of ParkerVision appear to make large amounts of stock available for loan. Since the stock is such an obvious short, generally the stock is quickly taken and shorted. When the stock price needs a boost, sizeable and simultaneous stock recalls go out. This puts the stock on the SHO list, and over the next week or so the stock price rises - sometimes considerably. This generally coincides with a significant increase in posting on the Yahoo PRKR board. The price boost is often used to cover over bad news or lack of good news.
We caution anyone considering a taking a short position in PRKR to be careful. Make sure you have a solid locate. Below about 5M shares shorted there appears to be no problem, above 6M shorted you can count on a big recall, between the two is the grey area. This behavior appears to be semi-legal (unless Jeff Parker is involved in organizing the recalls - in which case there are serous question of Reg FD).