You have inadvertently activated the "search with scan" feature for "custom search 8". This feature can be activated for any service search or custom search "band". It is a nice feature, but it can also be annoying if you enable it by accident.
To disable it, press/select: MENU > Search For > Edit Custom > Custom 8 > Search with Scan > Set Lockout > Lockout.
From the last sub-menu you can also assign it a quick key which you can use to enable/disable a search band like any other system. This is handy if there is a service or custom search that you routinely wish to listen to, but not all the time.