In the recent org-mode realease something recurring ranges with timestamps are not properly recognized in the agenda.
This wont work:
<2011-04-07 Thu +1w>--<2011-04-20 Wed>

Things get even messier when timestamps are involved: <2011-04-07 Thu 17:30-18:40 +1w>--<2011-04-20 Wed>

The usual fix is to use a diary sexp and put the time in the heading:

* 17:30-18:40 foo
<%%(and (= 3 (calendar-day-of-week date)) (diary-block 4 1 2011 9 30 2011)))>

Which in turn breaks exporting to iCalendar and is an ugly hack.

Unfortunately I'm not good enough at lisp to fix it myself, so I'd volunteer for testing if someone is interested to fix it. As I can see it their are multiple solutions: Either allow the diary sexp to use time or change the way the ranges work.