Search box does not follow the action attribute in the form

I have a problem in creating the search box template for my custom template (using Drupal 8).
Basically, the search box has the correct address in the "action" attribute of the "form" element (http://www.mydomain.com/my-site/en/search/site).
But when you click the search button the action url "becomes" wrong (http://www.mydomain.com/en/find/whatever).

<!--form--search-block-form.html.twig-->
<form{{ attributes.addClass('search-form', 'navbar-form navbar-search fnd') }} role="search">
	<div class="input-group">
		<input  type="text" class="form-control input-sm q" placeholder="{{'Search'|t}}" name="q" id="q" title="{{'Search in the website'|t}}">
		<span class="input-group-btn">
			<button id="sbtn" class="btn btn-sm" type="submit" title="{{'Search in the website'|t}}"><span class="glyphicon glyphicon-search" aria-hidden="true"></span></button>
		</span>
	</div>
</form>

Do you have an idea about this problem?
Thank you in advance