We use a combination of single issues and parent/subtask issues. Often the parent/subtask issues are used by us to indicate that when working on a change/bug(the parent task) we also tackle some other small issue (the subtask). When we look at the agile board, the only thing we can see is the status of the subtasks, not of the parent task. It is thus also impossible to drag the parent issue from one column/swimlane to another like we can do with simple issues or subtasks.

Especially when trying to see how far we are in the sprint, it would be good to see in which column/swimlane the parent task would fall.
I can imagine an indication like the one on the left hand side of the simple issue blocks (a colored bar, depending on the issue type), but horizontal on the bottom of the bar covering all swimlanes. The indication bar would then be displayed over the swimlane the issue is in.