Always-valid field with disabled checkmark does not work

[joskuijpers]

I have an optional field in my form (surname prefix 'von Damme' -> 'von' and 'Damme', very common in the Netherlands). I don't want to show a checkmark when no input is given, but the validation state must always be Valid so that an empty field is also accepted.

Sounds easy enough:

_prefixCell.validationState = BZGValidationStateValid;
_prefixCell.showsCheckmarkWhenValid = NO;

I do not use any validation block. It is however rendered incorrectly: it is indeed valid, but even before typing anything, it shows the checkmark.

Could you look into this?