Boil not casting if the opponent has no supports

Although the card description is quite ambigous (a la Anguished Unmaking or Torment of Hailfire), I was under the impression that Boil should cast even if the opponent has no supports in order to deplete the board of blue gems. Unfortunately, this is how it works:

0) There is no support of the opponent on the board (blue or not)
1) Boil is filled with mana
2) The system asks if you want to play boil - clear intention that it should be castable
3) You confirm

Expected result: Boil should cast, destroying all blue gems
Actual result: Boil does not cast

I recently obtained it (and never faced it in the past), so I'm curious if someone can confirm if this was its behaviour in the past or not.