We had a challenge today after we needed to move a issue that belonged to a sprint into another Jira project (a project without a scrum board). We then found issue was no longer visible on the agile board (makes sense in hindsight, since the board's filter wasn't looking in the project the issue was moved to), but the issue itself (per the issue's details screen) was still attached to the sprint.
We looked into ways to remove the issue from the sprint, and we found a solution to temporarily change our "edit issue" screen configuration (per this post - https://confluence.atlassian.com/display/AGILE/How+do+I+remove+all+Sprint+related+info+from+an+issue)
I'm a little reluctant to make this "edit screen" change permanently (I could foresee problems with allowing the users to edit the sprint ID directly). I guess the other (and perhaps easier) solution would have been to move the issue back to the original project, remove it from the sprint, then move back to the destination project.
Any observations / better ideas?