> Maybe you have the print dialog set to print 3 copies.
And that could have been set in the application printer dialogs, or in the operating system printer setup/preferences (or both, but then you'd get 9).
It can also be set locally on some printers, but I suspect that's not what's happening here.
Is everything in the book tripled-printed, or just some?
Is it printed cover-toc-body 3 times, or cover-cover-cover, tocx3, bodyx3?
Are other PDFs printing correctly to the same printer (using the same driver)?