Nodes beloging to multiple groups appear in Views as many times as current user's memberships

Problem/Motivation

Nodes beloging to multiple groups appear in views many times, if user is member of more than one of these groups.

Steps to reproduce

On a fresh install:

1. enable Group and Group Node.
2. create a new group type "Generic"
3. enable content type Page for that group
4. create two groups of "Generic" type: "GroupA", "GroupB"
5. create a new Page content "Test"
6. create a new View on nodes, with a page display, insert path (ex. "/test"), leave all to defaults
7. add "Test" node to "GroupA"
8. add a new user "UserA" and add to "GroupA" members
9. as UserA visit /test views page, there is only one node instance
10. now add "UserA" to "GroupB" members
11. again, as UserA visit /test views page (maybe you need to clear cache or save view). Now you see the "Test" node two times

Please note that the view hasn't any relationship, so i see that duplication as a bug.
I expect to see only one occurrence of every node that user has access to as per 1.x branch.

Proposed resolution

Flagging "Distinct" on views query settings can be a workaround but it is not a solution, expecially for more complex queries.

Remaining tasks

User interface changes

API changes

Data model changes