It is impossible to deselect an active ability if a champion or relic features no attack ability.

Reproduction Steps:
1. Deploy Elven Prodigy and Bridge to Nowhere.
2. Deploy Epochal Oasis to give Prodigy Teleport 2.
3. Use Rain of Arrows.
4. Select Teleport 2 by clicking the button or pressing 2 on your keyboard.
5. Elven Prodigy will be unable to cancel the ability use by any means, effectively forcing you to use teleport 2 and potentially waste 4 AP. Note that she can cancel it as long as she doesn't have rain of arrows on cooldown, which can be cancelled unlike TP 2 (most likely because it's an attack ability).
6. The same issue applies to Bridge to Nowhere, although there's no AP but CD waste instead.

Posted this here instead of regular bug reports, because this is an issue that exists only within the new client.

@Senshu @Sokolov @Wraith @TheBeeKing

 

i too have this problem sometimes, non attack abilities cannot be canceled by rightclick and only way to cancel is selectin basic attack. of course on a unit without a basic attack, that would be impossible, so you cannot cancel a wrong teleport etc...

 

You can cancel abilities like this by left clicking one of your runes in the deployable list on top. Just select one rune and it should go away. I have the same issue with my Firecases. Once leap is pressed for checking the range, you cant get out of it. I think its the same issue. Hope this helps.