I am typesetting a book, but the printers has sent it back several times, claiming that the page numbers are misaligned. Since I have centered the page numbers, this is confusing. But they provide pictures that overlay two pages and true enough. I rechecked and the page numbers in the master pages are centered to the margins. So I tried centering them to the pages instead. They came back from the printers with the same comment. I rechecked again. And it turns out that the page numbers were not perfectly centered. Indeed, all text written in any text frame in a master page is aligned about 0.5 centimeters from the left border of the text frame - and that is what the centering is based on. This means that the centering is always pushed a bit to the right. I have tried changing font and using normal text instead of page numbers. The result is the same. If I try right-aligning the page numbers, they are aligned perfectly. There are no blank spaces or anything else in the text frame. I have tried this in multiple documents and it's the same everywhere.
For now, the solution for me has been to left-align the text and then move the text frame to the left of the place I want it to be so that the text starts where I want it to be, but it's a hassle and is much less precise. It makes centering almost impossible, so I had to move the page numbers to the margins (left for left pages and right for right pages).
Is this a bug, a feature that I cannot understand the meaning of or something that I am doing wrong?
I use Scribus 1.4.4 on Ubuntu 15.04.
Thanks in advance for any help.