Validate-need with more than one option

I am able to validate-need one column in R, but not more. See examples below:

Works fine: validate(need(!(c("b") %in% c("a", "b")), "x"))

Works fine: validate(need(!(c("z") %in% c("a", "b")), "x"))

Not working properly: validate(need(!(c("b","z") %in% c("a", "b")), "x")) it should not validate and give an error, but actually it validates.

Thank you for your help