I have about 10m of WS2801 connected to my arduino.
At the start, middle, and end, i have connected more power to prevent voltage drop. All the grounds are common and the power is comming a single 12v power supply.
The strip responds to data and signal correctly. However, one pixel of the strip stays on all the time, very very dimly.
SO, if i choose RED, red will be very bight, but i'll still see a speck of Green and Blue lit up on the LED. If i choose Green, green will be very bright, but i'll see a speck of red and blue. The IC's before and after this IC work correctly. (this IC also works correctly, except for full off)
Off, their will a very dim speck of rbg light on aswell.
To double check, presuming your strip of LEDs is in more than one piece, you try swapping the order of the pieces. If the same LED retains the fault, it is clearly damaged. If the fault moves to another, then there is something very strange about your code. Almost certainly a damaged chip however.