It might also be the smells. When I change my hog's liner, I always keep something "dirty" in the cage so she has something that smells like her after the clean liner is put in.
I use a great liner that I actually bought from Nikki! I put the liner down in the cage, put smallish pieces of fleece in her igloo and her other 2 hiding spots, plus fleece strips (pieces of fleece about 1 inch wide and 6 inches long) scattered around her cage. She usually drags a lot of it into her igloo when she goes to sleep so she can make a pretty nice nest for herself and has enough fabric to burrow around.