For sure, the #1 most annoying thing about YT (done user story style):
1. Go to a ticket in one project (A), after possibly doing some stuff in another one (B)
2. Create a subtask
3. Figure out later that the subtask was created inside the other phantom project (B)
Seriously, supporting the possibility of a subtask being from another project is something that bends my mind in ways that are unnatural, but having it ever default to that makes zero sense.
Yes, I do realize that is my opinion.