Dedupe broken for some weight combinations

For e.g: when first name is absent in params for a fuzzy rule - first_last+email, queries would be generated as:
Array
(
[0] => SELECT id id, 5 weight FROM civicrm_contact WHERE first_name = 'NULL'
[1] => SELECT id id, 7 weight FROM civicrm_contact WHERE last_name = 'Adams'
[2] => SELECT contact_id id, 10 weight FROM civicrm_email WHERE email = 'adamsmelinda@npo.co.in'
)

Which would work with old union algorithm but not with the new one. And therefore would not give the correct results.

With new algorithm the queries should be generated as :
Array
(
[0] => SELECT id id, 7 weight FROM civicrm_contact WHERE last_name = 'Adams'
[1] => SELECT contact_id id, 10 weight FROM civicrm_email WHERE email = 'adamsmelinda@npo.co.in'
)

With "find dupes" also there is issue for weights of nature:
10,7,5 with Threshold 17 ( A threshold of 20 / 10 should work fine ).

weights of following nature should work fine:
10,10,10 with threshold 30 / 20 / 10
5,5,5,5 with threshold 10
...

Steps to reproduce
================
update default Individual Fuzzy rule slightly so that Threshold = 17 instead of 20. This SHOULD mean that if Last Name and Email match, we have a dupe. Create two contacts:

Jack Black, jblack@foo.org
Jackson Black, jblack@foo.org

The "save individual" form won't pick up the dupe suspect.
Running "Use Rule" from dedupefind, won't find the pair either.