Backport PR #36371 on branch 1.1.x (BUG: Fix MultiIndex column stacking with dupe names)
Backport PR #36371: BUG: Fix MultiIndex column stacking with dupe names
The failure is also on 1.1.x branch. https://travis-ci.org/github/pandas-dev/pandas/jobs/728460104

so merging otherwise future autobackports could fail with merge conflicts on whatsnew