Does Avenir display with italics as bold as well? If so, maybe just triple-check that you're on 2.8.1, not a previous version. The well known italics-displayed-as-bold bug was fixed with 2.8.1 in the standard firmware. I don't know about the patcher.
Also, check your fonts manually on a PC to see if they're labelled
completely correctly,
with the font name itself as the filename title, and-Regular, -Italic, and -Bold (and -BoldItalic, if present) appended.