gerrit generates spurious conflict on staging-approve, merges the change, fails to mark as merged in database

See revision 4 of this patch set http://codereview.qt-project.org/8131

• I staged the change, it started testing as SHA1 c966da875ae514c3ce0491445a88011b60afa00d
• Test succeeded, staging-approve was performed
• The change in gerrit received both a "no regressions!" comment and a "merge conflict" comment. The change was not marked as merged. I am not sure what two commits were being merged when the conflict occurred.
• Using git, it was verified that gerrit's master was now pointing at c966da875ae514c3ce0491445a88011b60afa00d (the tested and approved SHA1).

Overall state: change is merged, but it has an incorrect "merge conflict" comment and is not marked as merged in the database.