Automatic changements of Default Branche

Summary

We are using GitLab CE 8.11.8 on our server. Omnibus instalation on CentOS.

We have set the Default Branche in Project Settings. Under 'root' account. That works fine for few days and then , out of nowhere, suddenly, that Default Branche automatically changes , to some of our other Branches (like RC,QA,....), without any notification or reason. When our Developers create New Issues, New Branches are automatically created from WRONG Default Branche and later we have a lot of problems. We are having that problem already since version 8.7 when we started using it.

Expected behavior

**Default Branche should be steady, set manually by only 1 person with rights, and not that it changes itself automatically. **