Query builder weird behavior with boolean custom fields

Related to CRM-12712.

I am using the query builder with different filters on boolean fields and several things are not right.
In this case I am filtering by membership since, and by the boolean custom field "Member". I assume the bugs appear even if I was to search without the membership filter.
Search 1a:
Member Since > 20130217 ...AND... Member = No
=> 284 Contacts
Search 1b:
Member Since > 20130217 ...AND... Member = Yes
=> 190 Contacts
Search 2a:
Member Since > 20130217 ...AND... Member != Yes
=> 284 Contacts
Search 3:
Member Since > 20130217 ...AND... Member IS NULL
=> 26 Contacts
-> Note: These 26 contacts were not included in the 284 above!
Search 4:
Member Since > 20130217 ...AND... Member IS NOT NULL
=> 474 Contacts
Search 5:
Member Since > 20130217 ...AND... Member IS EMPTY
=> 310 Contacts
Search 6:
Member Since > 20130217 ...AND... Member IS NOT EMPTY
=> 190 Contacts

Issues:
1. Search 1a lists the same results as 2a, but 1a should actually also include the 26 contacts from Search 3 which have NULL values.
2. Search 5 (IS EMPTY) seems to apply no filter whatsoever – it catches Yes, No, and NULL
3. Search 6 (IS NOT EMPTY) seems to do the same as filtering by Yes.
4. After using the query builder with = Yes or =No on a query field, and the refining the criteria to IS (NOT) NULL, IS (NOT) EMPTY, the Yes/No operator is still shown in the list of criteria. So after searching for Member = Yes and then going to Member IS NULL, the UI will show "Member IS NULL Yes"