Does MOD operator work?

I just spent over an hour trying to figure out why MOD(appvars.avLatDecimal,1) was not returning the decimal portion of the latitude. I finally achieved the correct result (i.e. decimal) with a subtraction:

appvars.avLatDecimal - appvars.avLatDeg

(Previously to that command, I had set appvars.avLatDeg variable to the integer portion of that latitude.)

Am I missing something?