The RELEASE-NOTES-en.txt file contains control characters after every section number in the body of the text (i.e., not in the outline in the very beginning). If you less /usr/share/doc/fedora-release-4.91-1/RELEASE-NOTES-en.txt, you find stuff like this: 2.\001Overview of Fedora Core 4 test1 (yeah, it says FC4T1, but that's a separate bug :-) The \001 looks very ugly, more embarrassingly so in the installer release notes viewer.
Reassigning to a toolchain expert to see what is happening here.
I am seeing a 0xC2 0xA0 unicode sequence here, instead of the \001 you mention. Eterm barfs on it but gnome-terminal displays the text without any artifacts. This is probably a locale problem when generating the text file versions. I'll check further.