EDS + request parameters = fatal.noReturnURL

[Peter Schober]

(Sorry, seems it's my Struggle With EDS day.)

When integrating the EDS into a website (I could even reproduce it
with static HTML, like in the public example provided below) where
it's displayed on the front page of the app (not approached via DS
protocol) everything works fine -- except when
accessing the URL with (any) request/query parameters:

Works fine:
https://saml-test.aco.net/

Causes the fatal.noReturnURL error with the pop-up
"FATAL - DISCO UI:No URL return parameter provided":
https://saml-test.aco.net/?foo 
https://saml-test.aco.net/?what=ever&foo=bar
Consequently the EDS fails to render.
(When it fails I notice there's no request to the server for
/Shibboleth.sso/DiscoFeed after the initial GET, as compared to the
working case.)

Relevant (I think) EDS config:
this.defaultReturn = "https://saml-test.aco.net/Shibboleth.sso/Login?SAMLDS=1&target=https%3A%2F%2Fsaml-test.aco.net%2Fsecure%2F";
this.defaultReturnIDParam = null;
this.myEntityID = null;

The error does not change or go away when I set
this.defaultReturnIDParam = 'entityID';
(which should be ok as per my reading of
http://docs.oasis-open.org/security/saml/Post2.0/sstc-saml-idp-discovery.html )

Any suggestions?
-peter