Thanks goes to GreatBull who found the solution.
This patch also force the icons to be displayed in the buttons for the Linux system (already worked fine on Windows)
- Some theme names has also been rename for consistency:
"Focus" has been renamed to "25-Gray-Gray" and enhanced a little bite,
"01-Cookie-Dough" has been rename "21-Gray-Gray"
- Some unused files where removed.
Those themes has been tested successfully on my Ubuntu 11.04 system...