The copied threads hadn't a first_post_id set.
Because of this, you got an error while any moderation of the thread( e.g. setting prefix, moving thread, renaming it,etc....)
this is fixed now!
While the upgrade, all "wrong" threads will be rebuilt, so you'll not lose any data.
I really apologize for this.
also another minor design bug was fixes
New Feature => the thread copying will also be recorded inside the mod log