Note: Not a solution but marked as such to elevate a key reply. And I hope you don’t vote for this request!
Asana is helping us in a very thoughtful manner, and you’re all being ungrateful!
Let me explain.
Pause that typical blocking rule and add this one (as Active) instead, temporarily, as I just did:
Re-run the same test, marking Subtask 2 complete. What happens? The due date is updated, of course. And the subtask is not assigned to you.
Every bit of this makes sense to me and I congratulate the designers and developers.
Starting with the test rule: That operates as expected as I suggested above. Asana can carry out your wishes without assigning the subtask to you and it does.
Now for your example with the regular blocking rule: What Asana does in My Tasks in consistent to its behavior in projects for “Runs on tasks and subtasks” there. In projects, the subtask is not in the project but rules run on it because it’s a subtask. Similarly, in My Tasks, the subtask is not in My Tasks (assigned to me) but rules still run on it because it’s a subtask. We’re surprised that Asana assigned it to you, but it only did so because you asked to move it to a My Tasks section, and to do so it helped you out by assigning it to you to allow your wishes to be carried out.
I tested the blocking rule in a project (instead of in My Tasks) and sure enough it behaves consistently there: If the rule asks to move it to a section of the project, then it kindly does so–by homing the subtask into the project, the only way it can honor your wishes!
By the way, I guessed wrong to your test; I guessed that Asana would run the rule, but fail to make any change as a result of it because the subtask wasn’t assigned to you already, but I didn’t have enough faith in Asana and glad they handled this case. And if anyone wants to prevent it, just add a condition to the rule to only run if you’re the subtask assignee.
Don’t forget to pause or delete the new test rule and make active the original blocking rule.
Thanks,
Larry