Flask - WTForms uses as Submit Button of a Form this variable: {{ form.submit() }}

When I use this variable, the frontned generates this input field:

<input class="btn btn-primary" id="submit" name="submit" type="submit" value="Login">

Unfortunately the form does not respond until I double click on the input field.

MDB seems to respond only to button tags in the form.

<button class="btn btn-primary" type="submit">Submit Form</button>

If I use the standard bootstrap, then sending with the input field generated by {{ form.submit() }} also works.

Does anyone have an idea what this could be?