Why is the form submitted even if the Math is wrong?

Question

MODX

I connect ajaxForm like this:

[[!AjaxForm? 
  &form=`tpl.AjaxForm.5` 
  &snippet=`FormIt` 
  &hooks=`math,FormItSaveForm,email` 
  &mathMinRange=`1`
  &mathMaxRange=`10`
  &emailSubject=``
  &emailTo=`[[#8.tv_01]]`
  &emailFrom=`[[#8.tv_01]]`
  &emailTpl=`tpl.email.4`
  &validate=`math:required,name4:required,phone4:required,workemail4:blank,text4:required:stripTags`
  &submitVar=`form4`
  &validationErrorMessage=`В форме содержатся ошибки!`
  &successMessage=`Сообщение успешно отправлено`
]]

In the template, I set the captcha:

<div class="math">        
    <div class="math_1">
        [[!+fi.op1]] [[!+fi.operator]] [[!+fi.op2]]
    </div>
    <div class="math_2">
    <input class="form-control" type="text" name="math" value="[[!+fi.math]]" />
    <input type="hidden" name="op1" value="[[!+fi.op1]]" />
    <input type="hidden" name="op2" value="[[!+fi.op2]]" />
    <input type="hidden" name="operator" value="[[!+fi.operator]]" />
    </div>
</div>

The "math" field is correctly considered required, but the form is submitted for any value entered in it. What's the matter?