Update existed custom criteria value, invalid but saved successfully

Description

Steps to reproduce

1. Use code snippet bellow to create custom visitor group criteria.

public class CustomCriterionSettings : CriterionModelBase, IValidateCriterionModel
{
public string MyCustomProperty { get; set; }
 
public override ICriterionModel Copy()
{
return ShallowCopy();
}
 
public CriterionValidationResult Validate(VisitorGroup currentGroup)
{
if (MyCustomProperty == "dummyvalue")
{
return new CriterionValidationResult(false, "Invalid criteria value");
}
return CriterionValidationResult.Valid;
}
}
 
[VisitorGroupCriterion(Category = "Custom Category",DisplayName = "Custom Criterion",Description = "A descirption")]
public class CustomCriterion : CriterionBase<CustomCriterionSettings>
{
public override bool IsMatch(IPrincipal principal, HttpContextBase httpContext)
{
return true;
}
}

2. Create new Visitor Group.
3. Add CustomCriteria with value != "dummyvalue".
4. Click Save.
5. Reopen the recently-created Visitor Group, change the value of CustomCriteria = "dummyvalue".

Expected: Error message shown and VisitorGroup is not saved.
Actual: Error message shown but VisitorGroup is saved successfully.