Hello
Since my Thunderbird got updated a few odd things have happened. First my Runbox inbox and spam got moved to a separate branch of the tree view in the folder pane, separate from all my Google accounts and the sent mailbox appeared in Local Folders.
Not knowing your specifics, I would think that anything sent to your runbox address, or filtered to go there, would appear in your runbox inbox and spam would go in the spam folder for Runbox, so I’m not seeing anything odd. Thus, the question is, why is this odd?