I think the SQL statement creation for the case of 
matching a string property to a list of values is 
wrong. In rdbms_common.py, in the method Class.filter, 
the statement (line 2105 in version 0.85)
where.append('(' +' and '.join(["_%s._%s LIKE '%s'"%
(cn, k, s) for s in v])+')')
 
should be 
where.append('(' +' or '.join(["_%s._%s LIKE '%s'"%
(cn, k, s) for s in v])+')')

as the documentations suggest:
The filter must match all properties specificed - but 
if the property value to match is a list, any one of 
the values in the list may match for that property to 
match.

Best regards,
George