Short description of error
Normally lattice controls both emitter and particles, but disabled Lattice modifier affects particles only, without emitting object. This is cool feature, but there is no information that it could behave like this.
I think, if something is disabled - it shouldn't confuse things.
Exact steps for others to reproduce the error
Just open the file. Another way to reproduce this feature is to enable Lattice modifier, but set Strength slider to zero.