I've added a simple regression test for sorting dates, one of which is a
NULL value. Works. So this is *not* in the roundup API,

Please look for testDateSort in test/db_test_base.py

This contains code you can use to check if this behaves differently in
your installation with your particular date attribute and your version
of PostgreSQL. 

My current guess is that your template is doing some weird things and
tries to sort date values in the template. Can you give us the template
that reproduces the problem?

@David Murray: You mention Multilinks: Yes these *are* sorted in python
because it isn't possible to do this in SQL. You should not allow
sorting on multilink values via the web-interface if you can avoid it.
But I don't think (at least from the description I've read) that this is
the problem in this case.