Hi! Problem solved. It has nothing to do with XFree86 version. It was due to installed fonts. Installing xfonts-greek-ph-scalable and xfonts-scalable-nonfree and restarting xfs then the X server seems to have solved the problem. However, I made other changes so I'm not 100% sure (downgrading xfree86 from 4.3.0-pre1v1 to 4.2.1-11, removing some fonts, ...).
Sorry for the noise, Lucien.
