Javascript (with dijit.form.NumberTextBox) variable / 'NaN' behaving weirdly

I have a couple of dijit.form.NumberTextBox, Which return javascript Number values if valid data is in the textboxes, otherwise NaN. I get this strange behavior. When I checked in firebug (both the textboxes are blank):

>>> hours
 NaN
 >>> minutes
 NaN
 >>> minutes == NaN
 false
 >>> hours == NaN
 false
 >>> hours == minutes
 false
 

Why is it behaving so?

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