Cursed Ground sometimes doesn't appear, despite using mana

It seems like the terrain sometimes prohibits cursed ground from being created, such as narrow areas and stairs, despite spending mana. It gets very frustrating having to repeat the curse 3+ times when the curse costs over 600 mana, which is most of my mana pool. Hopefully someone can look into this.

yes it is a super annoying problem in tight maps
because it uses the mana but lays no curse