The svg is limited to palette button use, we use the denemo font in menus and tooltips.
You said that you tried a modified denemo font which would make it clear if the denemo.ttf was actually being used and it seemed that it wasn't - the modification didn't show. It would be easy to be tricked in this test by the presence of an old denemo.ttf somewhere on the machine ... are you able to search to make sure?
The fact that changing the prefs->Miscellaneous font to a larger size worked would mean that our call to set the default is being responded to - that it can use the size request but didn't find the font.
(I guess you know that it is not the filename that is used to find the font, but the internal name inside the file, so you can't hide a font by re-naming the file?)
Did you say other applications list the denemo.ttf font (is there a character map tool like on Debian and windows?)
Richard