What is supposed to happen is that everything, objects and textures, respond to snowline in the same way.
Imagine you have a hill with a peak at +100 m, but you have set the snowline to +50 m, which should produce a snow-capped hill with both objects and textures snowy at or above +50 m.
As it stands, only the objects above 50 m get snowy, the textures don’t. To also force snowy ground texture, you must set the snowline at 0 m (or less). So the +100 m altitude hill with snow on the ground just on the hilltop is not possible due to this fault.
.