See title. Is this behaviour intended or more likely a bug?
Im on Mac Version 2.2.2.
Hmmn. On my Mac running 2.2.2, I just created a new note with a new tag, then changed the tag. It all worked as expected. Have you tried restarting to see if that fixes it?
I’d expect the note to remain open and Notes selected in the sidebar. Maybe this is happening under some specific conditions?
I’ve managed to reproduce the “bug”.
I have the tag #bugtesting, inside it needs to have at least one note with the tag #bugtesting.
And I have the subtag #bugtesting/subbugtesting.
If there is only one note in the subtag #bugtesting/subbugtesting and i delete/change the tag #bugtesting/subbugtesting inside the note. (You also need to select the subtag in the sidebar. If you dont select it, then this bug won’t happen). Then the note closes itself, and the sidebar focus is now on all notes.
One more thing to add:
If i have one note with the tag #bugtesting and one note with the tag #bugtesting/subbugtesting. And i click(focus) on the tag #bugtesting and then delete the tag “#bugtesting” inside the note. Then this note also closes.
The tag in the sidebar remains, because the note with the subtag #bugtesting/subbugtesting still exists (as it should be). And the focus of the Sidebar is still on #bugtesting.
I think I got it. Just to be sure, do you have preview style > Hide subtag notes active in your note list menu here?
yes I do!
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Deactivating the setting “hide subtag notes” only fixes half of the Problem. The bug still exists, if you select the subtag #bugtesting/subbugtesting and delete the subtag inside the note.
Similar (old) bug is there when you select a note from the Notes/Todo in the sidebar:
When you check the last item in the notes’s todo list, the note disappears from view in note list, but also dissappears from the editor!! – Quite confusing and annoying:
I might like to also add a comment or more text in this note after I have completed all the todos. Now I have to switch to all Notes in side bar and reopen the note from there 
I would expect focus on note to shift to all Notes (top level) in sidebar, and even more importantly: note to stay open in editor, so I can continue to edit, even after completing all my todos in that note.
Hope that can be fixed soon 
PS. This bug is on MacOS, iOS and iPadOS in 2 and 1 pane views only.
On Mac it’s sometimes even more puzzling: The note sometimes stays, and sometimes disappears form editor.
But when it disappears from editor, you get a blank editor pane and can start writing, but this is a “ghost note” that disappears into thin air when you leave it, and can nowhere be found afterwards
See video: