This explains our lily. It would send 3 or 4 large leaves to the surface and was growing like crazy under the substrate as well. We began trimming it down to 2 or 3 big, healthy leaves to let some light to the plants below. Then, for about 2 months, it decided on it's own that 1 surface leaf was enough and began sprouting leaves 4 to 6 inches high, so we just let it be.
Eventually, it let go of the surface leaf and has been slowly bushing out at about 5 inches above the substrate for the past few months.
Thanks for the explanation.