In my flow I essentially only ever merge by copying the task ID, so the filter doesn't matter at all. Do you tend to search for the task by name?

My flow is pretty much:

• Open a new window.
• Search for the original task. Usually this is one search, but sometimes I don't remember the name of it and this takes a few queries or I have to use a subfilter like "Author" or "Tags" or "Subscribers" or something to narrow it down.
• "Merge Duplicates In" on that task, pasting or typing in the task ID from the other window which is still visible on screen.

Since task IDs bypass filters the filter doesn't matter on this flow.

Are you generally, e.g., memorizing the name of the task, then doing the rest of the workflow in the same window?

I do think "All Open Tasks" (or maybe a hypothetical "Tasks I Looked At Recently") is probably a better default in the abstract, but there's a task somewhere about replacing these filters with the user's own search filters, which would tend to prevent us from guessing which filter to use (we could maybe make them stick per-dialog, I guess?).

I think this default ("all my open stuff") is probably the right one for "Edit Dependencies" and "Edit Maniphest Tasks" from Differential, and for "Edit Blocking Tasks", "Edit Pholio Mocks" and "Edit Differential Revisions" in Maniphest, although the argument for some of those is a little weaker.

T7805 was the "use applicationsearch in the dialog" task.

My workflow is find the parent task, click merge in, then select all open tasks and 9/10 times it's in the pane, select and go. I generally don't copy and paste the task ID. I don't always know if I'll find a duplicate, so I don't always copy the task ID before searching around.