Found this topic whilst searching for a solution to the same numbering issue on 1.4.6 - my solution is a little more precise and may help others:
TL,DR: Use Style Manager to manage your styles, avoid any manual styling of frames for page numbers.
Creating a book with front matter + content + back matter and differing numbering schemes - my front matter numbering was producing exclamation and question marks, Here's the setup:
Document:
Section | Content | Page range | Numbering | Master Page | Paragraph Style | Converted PDF Output |
A | Front Matter | p1-p4 | No numbers | Front Matter | Content Footer | left aligned exclamation |
B | Front Matter | p5-p10 | roman: v,vi,vii .. | Front Matter | Content Footer | center aligned - exclamation marks in out: '!,!I,!II, ...' |
C | Normal | p5-p10 | numeric: 1,2,3 .. | Normal Left & Right | Content Footer | center aligned numbers |
- Numbering sections - one covering A & B starting at 5 and one for C.
- Style: Content Footer - EB Garamond 12 Regular @ 10pt size, All Caps (I was using the same style for header & footer throughout).
Everything displayed fine in Scribus. It was only on export that the problem occurred.
I'd edited the style and switched to using EB Garamond 8 Regular @ 10pt size - because the floral decoration glyph was different between the two. At some stage I had manually edited the style on the footer frame in the front matter page - it was using the '12 Regular' style - overriding the paragraph character style. As soon as I re-applied the Content Footer style to the frame on the 'Front Matter' Master Page - the problem disappeared, A was blank, B was roman numerals. Manual editing of the frame style on the front matter causes the output to revert to the problem characters.