Bug during sprint completion - issues not moved to the new sprint

[Dominik Helber]

We faced now multiple times the following behavior.

During completing an active sprint, it has been chosen to move open issues to the new sprint. Unfortunately the issues have not moved to the new sprint, they ended up in the backlog. 

It always happened in the same Jira Project. The board has parallel sprints running. 

Does someone had the same bug or knowing why this is happening?

Thanks!