I live in a three year old house. About 6 months in we noticed a leak under the tile shower. The builder's tile man came out and made an attempt at repair and a year later we had the same leak again. He then tore out the bottom 18" or so and replaced the liner and re-tiled. To my knowledge there's been no more leak but through a hole we cut in the sheetrock in the abutting closet we see mold growing between the shower liner and what I think he called durock.Reaching in, I can feel moisture in the liner (the part that wraps in behind the "durock". I watched the second construction of the floor and don't remember a "pre-slope" that you refer to in other discussions. Is that a possibility or does anyone have other suggestions as to what is causing the mold? Where do I go from here? Do I have to tear it out again?

The mold is most likely from the shower pan.
Can you tell if the pan liner is flush to the subfloor? If so, thats not good.
Probably no vapour barrier between the cement board and studs. Also not good.

Sounds like a tear out to me.

w/ out a preslope moisture will probably condensate even through the liner, or if he didn't waterproof the cement board then moisture runs down behind the liner to where you're able to see, where the fungus is. perhaps I'm a big fan of putting heavy-duty fans and exhaust in showers. Perhaps the copper pipe is condensating?