Undo spells without a price.
You can do it with troops - why not spells? I know people may queue spells to store gold whilst they're gone for a little while (not that it matters now since they're 30 or 45 minutes each) and it may result in misuse. People can still store wallbreakers in barrack and hide elixir. This is not so much of a massive problem for me, but there have been times where I've mis-clicked a spell and then couldn't proceed to remove it due to not wanting to lose gold. Even when I've tried to click the information button for a spell I haven't seen the stats of for a while I have also accidentally tapped it into creation.
Just a thought, it would be nice for some folk playing if this wouldn't be a problem.