About a year ago, we were struggling with a git-review bug that caused lots of bogus warnings to appear. When running "git review", you'd get a warning saying you're about to submit multiple commits, followed by a list of lots of other people's commits that have already been merged. I fixed this in https://review.openstack.org/#/c/6741/ last year.
This bug is now back in the latest release of git-review that came out over the weekend. I complained about this at https://review.openstack.org/#/c/20450/ , which is the change that reintroduced the broken behavior. We are suffering from it disproportionately because we have defaultrebase=0 set on most of our projects, and the bug only triggers when rebasing is disabled (using either that setting or the -R flag).
The workaround is the same as last year: if git-review complains and you see bogus commits in the list, respond "no" to abort, run "git fetch gerrit", then rerun git-review. This will ensure git-review has an up-to-date view of the remote master.
Roan