One problem nagged me for a week, and I almost gave up, considered to distrohop from Debbie 4. I searched for a solution online, but didn't find it. Luckily, I found it myself. It was a wrong-fonts-in-a-wrong-directory-solution.
All I had to do is to remove TrueType fonts:
cd /usr/share/fonts/opentype
sudo rm *.ttf
All nice now. The intruder characters are gone.