Voltaic Mark not targeting correctly

The spell never casts on what my mouse is hovering over unless it is the only mob around. I have to aim my cursor slightly below the target for it to target what I want targeted.

I can recreate and work around it, but this cannot be the way it is meant to work.

It seems the mark always wants to target what's above the cursor instead of what the cursor is touching.

This makes it a roll of the dice in most cases if you are actually able to hit what you actually want to hit if the creatures are tightly clumped up.

All other targeting abilities seem to work correctly. Whatever the tip of the cursor is touching, is what gets targeted.