Problem with url_for and /showcases redirect

[torfsen]

I am dynamically constructing links for listing showcases by tag:

<a href="{% url_for controller='showcase', action='search', tags=tag.name %}">{{ h.truncate(tag.display_name, 22) }}</a>

The url_for call returns an URL for /showcases (trailing s):

http://localhost:5000/showcases?tags=interaktiv

That URL is then redirected to /showcase (no trailing s), but the query parameters are lost:

Either the redirect should also forward the query parameters or url_for should return the correct URL. What's the rational behind having both /showcase and /showcases?