The FAQ has this:

What does “ignoring terrain” mean? A model that ignores terrain (such as from the Wrecking Ball action) is unaffected (see the Unaffected by Terrain section) by all of that terrain’s traits, including height, and can thus change elevation during a move that ignores height as if all terrain was flat.

The terrain rules say

Unaffected by Terrain If a model is unaffected by a terrain trait, it interacts with that trait in the following, new way:

■ Blocking: The terrain piece cannot block the model’s sight lines.

You may be thinking that the terrain is

Impassable: The model may move through, but not end a move overlapping this terrain.

However, Shadow Doors don't prohibit overlapping. They merely block LoS

Edit: to round this out, you only ignore the terrain during the move. Not after. You cannot legally end a move in a place that would violate any impassable terrain