Views filtering fails in PostgreSQL

I've recently switched from MySQL do PostgreSQL drived Drupal. I'm using workflow for content creation management. In views, I'm filtering the certain node type (project) using workflow state:

SELECT DISTINCT(node.nid) AS nid FROM node node LEFT JOIN workflow_node workflow_node ON node.nid = workflow_node.nid  WHERE (node.type in ('project_project')) AND (workflow_node.sid = 2)  GROUP BY nid

This query fails with error: column reference "nid" is ambiguous. I'm not fluent with Views API, but I guess, the issue I'm reporting could be fixed somehow in Workflow Views handlers, responsible for SQL query creation. What I observe is:
- switching off distinct node selection fix the problem, i.e. the query fails due to SELECT DISTINCT(node.nid) AS nid
statement
- changing the grouping to GROUP BY node.nid also fix the problem.

So, I think, the best thing would be to group by node.nid, but I have no idea where to put the proper change in workflow views handlers..