Filter results affected by board grouping - but why?

[Niklas Malmberg]

We're running a Team-managed Jira SW project, with a sprint board.
On the board, we have created a column (state in item workflows) called Code Review, it's where we signal that another developer should do a peer review of the code.
 
I have created a custom filter "Show Unassigned CR" so it should be easy to find these tickets that have not yet been assigned.


And this worked just fine. Except when it's a Task or Story that has subtasks... 

First example: two tickets correctly found. Note the grouping = None


 Second example, board is now grouped by Subtask (which is my normal view, I like those swimlanes to keep Tasks and Subtasks together). Then one of the Tasks are no longer found! 


So, with board grouping set to Subtasks, there are two different ways a Task(or Story for that matter) can show up:
a) If a Task has subtasks, it will appear as a swimlane,
b) If a Task does not have any Subtasks, it will appear under Everything else.

And it turns out that only the b)-Task can be found when the filter definition above is applied (if other conditions are met of course). The a)-Task will be (wrongly) hidden by the filter, although all conditions are met.

Now why is this? 

[David Nickell]

A theory .....

does the subtask meet all the filter criteria?  Do you have a subtask status of "Code Review"? is the Assignee empty?   

I think the subtask has to make it through the filter on its own..  When you group by other attributes, I guess the subtask gets included as an "addendum" to the issue.

If you group by subtasks, I assume the starting point are subtasks that are valid in the filter.

Hope this helps