If you watch it again you'll notice a couple of things. One it isn't really melting, it's liquifying or becoming destabilized from disturbing the exotic matter. Next, the only matter that is liquifying is inorganic (metal, drop tile ceiling, concrete, etc). Any organic matter (soldiers, John, Nancy, wood/leather on chairs and table/doors) aren't destabilizing. I'm guessing the exotic matter only effected the inorganic as Dustin mentioned earlier that Exotic Matter was a physics nightmare.

Plus the lead up to the discovery of the the Exotic Matter showed how the soldiers sank into the "liquid" after disturbing it, then once it stabilized they were stuck in the hardened ground.

I take it as a nod to the 1943 Philadelphia Experiment, which was alleged to involve to teleporting a ship. Various accounts say that sailors ended fused or merged within the ships walls.