Various spells in the game have a directional cone or column AoE. The displayed AoE behaves strangely around impassable terrain. Target a spell like Fan of Flames at an impassable cliff and the displayed AoE is strangely distorted as shown in the image:

 

 

Column base AoEs have the issue that they often appear shorter than they should. I'm not exactly sure what causes this, the image below shows an example with the Rolling Flame spell:

 

 

There is also the issue that when casting some column spells my character has to move before casting them when I'm not expecting this. This happens particularly common with the Iconic Projection priest spell. It's possible the casting range is just set incorrectly.

 

 

Here's a video demonstrating how Iconic Projection bugs out against a flat area of navmesh