This switch does not allow you to choose which ports the default VLAN is connected to. Seeing that the configs for the default VLAN do get dumped into the config backup file, I decided to patch that file, modifying and uploading the internal config of the switch instead of politely asking it to remove that VLAN from some ports.
If you open the config file with a hex editor, you'll notice somewhere in the middle the strings "Default_VLAN", followed by the names of the VLANs