Exporting Membership custom data - missing correct column headers and data (3.4.5)

Problems:

When trying to export Membership custom data information...

1. exported membership related custom data is exported with column headers as custom_X ... instead of the correct column headers...
(where X is some number in the order that the custom data was created)

2. no custom data entries are exported - exported membership related custom data entries are all missing/blank

3. Under the page: Admin -> Configure -> Import/Export Mappings one or more blank entries are created (blank name, description and Mapping Type)

Steps to reproduce the problem on a new site / civicrm drupal demo site:

1. Admin -> Customize -> Custom Data -> New Group of Custom Fields (button)
2. Create a new group of custom data Used for Memberships... e.g.
Group Title Enabled? Used For Type
MailingDetails Yes Memberships Any

3. add custom fields...
e.g. Field Label Data Type Field Type Order Req? Enabled?
Copies Integer Text 1 Yes
DeliveryMethod Alphanumeric Select 2 Yes
MembershipDescription Note TextArea 3 Yes

4. add a new Membership for an individual...
e.g. (on the demo site) Alexey Kaminskij -> Memberships -> New Membership

5. add entries to the custom data fields for the new Membership
e.g. Membership Type -> General
MailingDetails -> Copies -> 1
-> DeliveryMethod -> by email
-> MembershipDescription -> This is a test

6. Save that

7. (Now try to Export Membership data...) In the menu -> Memberships... -> Find Members
8. Search
9. Select Records (e.g. All 31 records)
10. Change the drop-down menu (more actions) to Export Members -> Go
11. Choose Export PRIMARY fields or Select fields for export.... (pick the new custom data fields)
12. examine the CSV and the column headers for our new Membership custom data will be custom_5 custom_6 custom_7
instead of copies ; DeliveryMethod ; MembershipDescription

Forum REF - http://forum.civicrm.org/index.php/topic,11217.msg57790.html#msg57790