File saves "invoice" to document title. Trying to make it stop

I've got an invoice spreadsheet that saves the document title to whatever the first tab is titled.

If I save the document as:
Acme Invoice 12DEC12

when I go to retrieve the document, it's titled:
Acme Invoice 12DEC12 Invoice.

I could change the tab to: Horses

The file would automatically save as Acme Invoice 12DEC12 Horses

Where do I look to dig this out or disable it?