There is nothing wrong with email tagged [-SPAM-] appearing in your INBOX, the behavour will be consistent with that requested in your Spam settings. The logic is as follows.
If the spam applliances think the message is a bit spammy they flag it as (say) Level 5. Your settings request that any flagged messages are tagged [-SPAM-] on the subject line so that happens. Now the dealing with spam and aggressiveness filter settings come into play.
The former is normally set to "move to the spam folder". However only if aggreesiveness is set at a level equal to or higher than that of the message will it be moved.. Otherwise it is left in your INBOX with the [-SPAM-] tagging acting as a warning that the spam detection appliances think the message might be spam.
Having examined the message youself only if you think the message is definitely not spam should you report it as such. For example it might be from a mailing list you've signed up to and you are confident that a request to unsubscribe will be honoured.