form with FloadField required=false passes validation with wrong value

I have a form with

``` javascript
amount : forms.FloatField({label: 'Amount', required: false, maxValue: 1}),
```

When I input there randome string, like 'asdfasdf'
form.validate() returns true, form.cleanedData returns {amount: null}

When I input a big number, like 123 it throws me validating error "Ensure this value is less than or equal to 1."

Is it a correct behaviour ?