> My question is what happens when the syrup freezes?

Properly prepared syrup should never freeze.

When fed in the fall, syrup should be as thick as you can make it.  That is
usually around 67% sugar by weight or volume (doesn't matter which).  Sugar is a
natural anti-freeze. Cold syrup will get pretty thick, though.  Remember the
expression "like molasses in January"?   (But never feed molasses to bees, it is
toxic to them).

To make syrup this thick, hot water must be used.  The heat should be applied in
advance, since direct heat on the bottom of a vessel containing sugar can cause
carmelization which can be fatal to confined bees.

Just mix in a much sugar as you can and let the syrup settle.  Then pour off the
syrup to use for feed and use any settled sugar for the next batch.

Having said that, though I sometimes notice a sheet of ice on top of drums of
syrup sitting outside.  Rainwater or snow melt floats on syrup, being lighter,
and will make a sheet of ice.  This is a problem, since, even after it melts,
the water conceals the syrup from foraging bees, and unless they are gathering
water and thus reveal the syrup, they may not find it.

allen
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A Beekeeper's Diary: http://www.internode.net/HoneyBee/Diary/