False positive?

I took a clear blue easy digital test yesterday at 4:30 pm and it came out positive or 'pregnant' on the digital readout. I was so excited but thought I'd take another just to be sure. An hour later I took the second one and it was negative. I then took several others including one this am and it was also negative. I noticed that the digital readout on the pregnant test disappeared from the screen and the packaging says that the pregnant indicator would last for 6 months. Is that true? Wondering if that test should have read 'not pregnant' if it disappeared.