As far as i know its not mentioned in 7671 (certainly can't find the little rascal mentioned), its more of a building regs thing, if you google the key words you will find out more, insulation manafacturers worn about it (gypsom) , some polys are ok ie polyuerathane (spray foam) but polystyrene is a definate no.check what your blocks contain.
I have had this myself, i pulled up a water damaged chipboard floor layed on slabs of the stuff, it had only been down about 18 months and the cables that passed through it had already gone black and gooey.
I searched this forum and found this.
"In pvc cables a plasticiser is used to keep the cables flexible and its this plasticiser that migrates on contact with polystyrene causing the cable sheath to become sticky and eventually brittle."