Already closed issues reappear in started sprint

I have stories which i close as e.g. duplicated, they get removed from the planning board until i start a new sprint and some of those closed ones reappear in the freshly started sprint. i can not tell in which way they get added, must be due of some sorting (the issues are closed, no fixversion and without any labels). we have this issue since we moved to atlassian's on demand service. there might be an uncomplete filter query for the running sprint which we can not edit.

thanks for your help.