Logged In: YES 
user_id=1080231

I hacked the query directly within mysql and changed the ';'
in the date range into '%3B', then tried the query in the
web interface again. Calling 'issue.search.html' will show
<start date>;<end date> as it should. Evenso does executing
the query return with the correct result. So I guess that
this bug can be solved by replacing any ';' with '%3B' 
before storing the query.
A simple patch for 'cgi/actions.py' could be (based on 0.7.11):

Index: cgi/actions.py
===================================================================
@@ -137,7 +137,7 @@
 
             # The [1:] strips off the '?' character, it
isn't part of the
             # query string.
-            url = req.indexargs_href('', {})[1:]
+            url = re.sub(';', '%3B', req.indexargs_href('',
{})[1:])
 
             key = self.db.query.getkey()
             if key:

Regards,
Marlon