You need a mechanism to keep track of your unpredicted interruptions, so that you can improve your process continuously (which is what Kanban is about).
Moving items back makes this harder (although possible). What I saw some teams doing was to mark such items as cancelled, explaining in the tickets why they got cancelled, so that a manager can then see which columns (i.e. steps of a process) are interrupted more often. This could point to a bottleneck in this process.
In the near future, the "rest" of the cancelled ticket would make it back into the backlog as a new ticket entirely. This has the added benefit of keeping your backlog cleaner.
I will try this today with my own personal kanban board. I do find myself with cards moving back and forth a lot. The way I've dealt with "Cancellations" is I have a list called "Waiting" where I stick tasks that are blocked. Sort of like pending review but it could also involve waiting for a resource, a response, etc.
I think if I implement cancellations with details it could help me figure out what processes are broken that caused fires(i.e. this report is suddenly due, overriding everything else. Did I miss a memo? Do we have a solid process for anticipating these sorts of reports in the future? etc.) I could then go back during some planning time to view what needs some brain time.
Moving items back makes this harder (although possible). What I saw some teams doing was to mark such items as cancelled, explaining in the tickets why they got cancelled, so that a manager can then see which columns (i.e. steps of a process) are interrupted more often. This could point to a bottleneck in this process.
In the near future, the "rest" of the cancelled ticket would make it back into the backlog as a new ticket entirely. This has the added benefit of keeping your backlog cleaner.