List endpoints requiring POST method do not work

[testgonzo]

None of the following add or remove members to list endpoints work with this api interface:

POST lists/members/create
POST lists/members/create_all
POST lists/members/destroy
POST lists/members/destroy_all

Consistent code 112 ("You must specify either a list ID or a slug and owner.") error message though api calls are well formed. Believe the problem is related to how headers are formed when posting to endpoints?