Subject: Why does butter, when warmed in a microwave oven, melt from the inside out?

Most solid objects, when heated in a microwave oven, appear to warm from the outside surfaces first, with heat gradually being conducted into the center of the object.  
An example of this is a frozen piece of meat, which will soften on the outside surface first.  
One obvious exception to this appears to be a block of cold butter, taken from the fridge and placed in the microwave.
If it is left in the oven for a few seconds too long, the INSIDE of the block liquifies and runs out on to the plate,
leaving the outer form of the butter block intact.

I suspect the reason is that the microwaves heat water molecules and the outer surface of the butter is drier than the inside,
therefore the inside heats faster.   I have not been able to confirm my theory with anyone.  Can you help?

Thank-you.

Re: Why does butter, when warmed in a microwave oven, melt from the inside out?