I am having the same problems as little val. I have my shower leaking through the ceiling onto my kitchen floor. I have had the floor around the tub recauked and still leaking. I have tested my tub by filling it with water and draining it - NO LEAK. I have tried running the shower without anyone in it - NO LEAK. It only leaks when someone is actually taking a shower. What in the world could the problem be? I am freaking out because I have already put a lot of money into this. Is there anything I can do on my end? Please help!

Sounds like you have a improper seal around the tub and the only time it leaks is when someone puts weight in it
Sometimes I've seen them leak because tub was improperly set and when you stand in it it will actually drop a quarter of an inch at the seems also check your grout on the tile for cracks if none of this helps you're going to have to cut a hole in the vicinity of the leak and visualy inspect with shower running and some one in it at any case you'll find it with hole cut if improper set has occurred then your going to have to pull tub and relevel floor
Also check tub drain and tub diverter valve you should be able to see it with hole cut make shure person in the tub walks up and down the tub while your looking helps if you got a cell