Normally I have LANG=De_de and the kernel parameter
vt.default_utf8=0. E4 codes Umlaut-a in ISO 8859-1.
The bug occured in a real world situation (the file was
"mär19"). To reproduce on other keyboards: "touch $(echo -e
\\xE4)" and "nano $(echo -e \xE4)" work. "ls" shows the
filename correctly.
For another test, I changed set LANG=C in
/etc/default/locale and rebootet withou the kernel paramter
vt.default_utf8=0. This did not influence the bug.
I have tried older versions of /usr/bin/emacs-gtk (without
installing the whole package) down to 1.25.2+1-11. They show
the same bug.
meld is also a gtk-editor. But "meld $(echo -e \xE4)"
works fine.