Wicket-Ajax-BaseURL encoding problem when uploading file using ajax

Hi,

I have a strange error when uploading file using ajax request. I have
a page with parameters whit url like:
http://localhost:8080/myapp/customer/id/1234

When I am opening a modal window with upload form the Wicket-Ajax-BaseURL is:
customer/id/1234?1
and all links in ajax response are properly constructed, eg.:
../../wicket/resource/org.apache.wicket.ajax.AbstractDefaultAjaxBehavior/res/js/wicket-event-jquery-ver-1409306560000.js"

But when I choose a file and press upload (using AjaxSubmitButton)
then in the followed request Wicket-Ajax-BaseURL is encoded like:
customer%2Fid%2F1234
so the code inside UrlRenderer.renderRelativeUrl does not find a
proper baseUrlSegments so the calculated renderedUrl is wrong. This
leads to invalid url paths, eg.:
./wicket/resource/org.apache.wicket.ajax.AbstractDefaultAjaxBehavior/res/js/wicket-event-jquery-ver-1409306560000.js"
and other errors with resolving urls.

I cannot find where this base url can be broken? Maybe the problem is
somewhere in my code, but I don't know where to search for this.

PS. The same error is in FF and Chrome. Wicket 6.17.0.