Hmm ok. Think I've tracked it down to MtBdLfRg.ttf as the default font, and it is included in the source package ... so ... ok stumped as to why it renders differently to the official viewer.
Any clues?
Oh and while I have a totally abandoned thread to play with

Am I right in thinking that when I run a client I've compiled from source it doesn't upload crash information? I usually have it set to auto upload, and watching my net activity nothing seems to go out on my compiled clients.
Ok and a tweak for you to play with...
If you go into the client directory then 'fonts' you can replace the standard one and have a play with other fonts without re-compiling the client.
MtBdLfRg.ttf = The bold standard font
MtBkLfRg.ttf = The regular standard font
profontwindows.ttf = The script editor font
If you put a .orig on the end of the original fonts you can easily revert back. And I use symlinks to replacement fonts to test them.
So far Tahoma does a pretty good job of replacing the regular plain font even at tiny text sizes. Am thinking that the Linux standards DejaVu and FreeSans family might do well.