Same here, but i am on the way ;-)
In the file
/roundcubemail/program/steps/mail/sendmail.inc
there's a line at the end:
rcube_iframe_response(sprintf("parent.$JS_OBJECT_NAME.sent_successfully('%s');",rep_specialchars_output(rcube_label('messagesent'), 'js')));
It produces the JS-command in the selected language. Sample: "parent.rcmail.sent_successfully('Nachricht erfolgreich gesendet');"
If i send this by the js-console directly to the page, the page reloads and all works as it should. So the question is, why roundcube hangs at this line and does not send the js-command?!
It seems that the function "rcube_iframe_response" is not called...
[update]
The function "rcube_iframe_response" is called after all, but why does the js-command does not reach the browser?! :-(
[update2]
Also the new page (which should generate the "email sent"-message) is created successfully by the script:
RoundCube Mail
But my browser is still at the same page and does not update it...
And now i dont know further :-/
Any ideas?!