When I use an Ominous Trial Key on an Ominous Vault, it doesn't open.
BUT, when I use a normal Trial Key on an Ominous Vault, it DOES open.

I have no idea why this happens, maybe it has something to do with the fact that I used the following command to place the Ominous Vault:

/setblock ~~~ vault ["ominous" = true]

\/(l_l)\/