Maybe I need to better understand each panel.

Backburner: User stories that may or may not ever get done as the "priority" on these is currently too low to make into a sprint any time soon.

Backlog: User stories that are up next to be added to a Sprint or on a sprint but not yet complete.

Sprint: User stories currently assigned to a Time Blocked sprint for a Sprint Team.

So, how can a user live in more of the above in the backlog manager, or is it a bug if this is the case?