Should maple syrup be stored in the refrigerator?
I'll assume that you're talking about pure maple syrup in a glass container; if it's that adulterated pancake syrup then it's probably riddled with preservatives, so any advice here doesn't apply.

Pure maple syrup can and will grow mold on the surface if left in a cupboard.  There are several reports of this happening, and although several of those people say that it's OK to simply strain the mold and re-boil the maple syrup, (a) I wouldn't chance it, and (b) that process is hardly any more convenient than simply taking it out of the refrigerator a half-hour earlier and letting it come up to room temperature.

Maple syrup should be stored in the refrigerator.  It doesn't have to be, and it will probably take at least a year for it to grow any mold if left in the pantry.  But it will last longer in the refrigerator; I've seen refrigerated jars 3+ years old without any mold.