Hi and thank you for your inquiry. From testing the Visio Unsupported plugin with the version showed in your result, we were unable to replicate this issue. The service pack level is determined based on the version identified, so it does appear the detection script is properly working in our testing. At this time, I'd recommend you verify that the latest plugin updates are installed as well as the most current version of Nessus. Info on updating your plugins can be found at Documentation | Tenable Network Security.
If after updating the plugins, you continue to get the same result, please message me with a copy of the Nessus DB (database) scan results. This can be obtained in the web interface when viewing a scan result for a target host. You will see 'Export', which will have several options under the drop down. Choose 'Nessus DB' and you will be prompted to supply a password that will be required to open the result. When sending the db, you'll need to supply the password you set for the scan result. Note this can be any value and something like 'Nessus' or 'support' would be sufficient.