There aren't any options that relate to the setup of the forum that should prevent a thread from being created. It may be possible that there's another issue masking the problem.
If you can still reproduce it with your desired config, please submit a ticket with admin CP details and FTP details (note I may need to create some test resources to check it).
Also note that you can set permissions to remove the ability for people to post new threads in the target forum. The resource threads will still be created.