Issuable filter erasing milestone filter parameter

Summary

When filtering issues/merge requests it erases milestone filter when filtering by label.

Steps to reproduce

Go to any issuable list page, for example:
https://gitlab.com/gitlab-org/gitlab-ce/issues?scope=all&state=opened&utf8=%E2%9C%93&assignee_id=0&milestone_title=%23upcoming
Try to filter by any label and it will remove the milestone filter

Expected behavior

It should be filtered by label AND milestone