You got me.  Technically, both spellings are correct, but the words mean different things.  I goofed.  you caught a usage blunder rather than a spelling blunder:

USAGE The words discrete and discreet are pronounced in the same way and share the same origin but they do not mean the same thing. Discrete means ‘separate, distinct’ (e.g. a finite number of discrete categories), while discreet means "careful, judicious, circumspect" (e.g. you can rely on him to be discreet). 

Thanks for keeping me in line!