Fairly new to RH, I am experiencing this recreating old Win help files which we have lost the source files for. I managed to work round this by coding the special characters. Really tedious. Hoping there is a simpler solution.
I've experienced this problem in a different context. It's actually caused by an incompatible file encoding.
If you're a Mac user you can use these instructions for changing the file encoding (I had to change to ANSI encoding, but you might need to change to UTF-8).
If you're a Windows user, you need an advanced text editor like Notepad++ to be able to change the encoding.