Leaking tile clips are a common problem. They sit in the water course (where the tiles lap on the side) when water runs down the water course it hits the tile clip and drops into the ceiling space. 
over the years it will break down the plaster board and eventually break through and make a hole. there are a few types of tile clips The only real way to fix them is to replace them with a different type of clip which looks like a wire (just as effective in relation to hold down capabilities) See image below.
