[Bug] If I lower terrain to flat, my units still won't walk over them

I spent like 500 mana and couldn't get through, also lower land needs to affect 4 tiles instead of 1, casting the spell like 10 times is annoying.

I have to second (or third) this.

Currently cut a path straight through a mountain area and still couldnt get through, even when trying to walk the unit square by square and the path was assuredly flat. Used about 7 casts to make certain there was a chunk of flat terrain with no result.

I did this, too. What appears to have happened is that the ground is cosmetically flat, but logically still mountains. You can tell if you hover the mouse over the terrain, and look at the terrain info on the mini map.

My game is modded. Is yours?