This is fixed in current code by handling the exception:

            elif isinstance(propclass, hyperdb.Number):
                if type(v) != type([]):
                    try :
                        v = v.split(',')
                    except AttributeError :
                        v = [v]
                l.append((OTHER, k, [float(val) for val in v]))

looks like it's part of:

changeset:   4364:0e81742d0e2f
user:        Ralf Schlatterbeck <...>
date:        Fri Mar 05 14:22:34 2010 +0000
files:       roundup/backends/back_anydbm.py test/db_test_base.py
description:
- unify number searching across backends