Does antifreeze evaporate? My Rancher 420 sits most of the time as I hardly get to ride and I've noticed that the antifreeze is disappearing. Is this normal?

It happened when I bought the unit and I was told to flush it and fill with racing antifreeze (pink stuff). I did a year ago, but now I notice that months later the level is dropping below the fill line by 1/2". I checked the oil and it looks great and does not smell. Anyone seen this before? Dealer says it's normal.