One additional observation, while reproducing: If, before step 7, you mark the “Backlog” bucket in the clone as default (i.e. you do explicitly, what should have happened while cloning), bugs 3 and 3b do not trigger.
I was able to fix the bug where the default bucket would not be set correctly in 8da1102204.
All other bugs are now fixed as well (84cbd25e67). It was caused by a default filter done = false (only show tasks which are not done) when updating the bucket.
Please check with the next unstable build (should be ready for deployment in ~45min, also on try).