Thank you for providing the sample. The behavior you have described is caused by the value binding declaration. When binding is specified there should be no space between the value: and the field name. This is required as the validation is executed via the attribute name thus will not work as expected in this case.
Also you may know that there is no need to specify the value binding explicitly as the attribute will be generated automatically using the input element's name attribute. Here you can find a modified version of the jsfiddle you have sent us.
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