Characters sometimes change??

I am added onto a fixed width font a variety of special characters. As I’m nearing the end of creating them all, I notice that some of the characters seem to change into something completely different in the “Test Font” window than what they should be. If I remove some characters (that is, delete them from the font), these characters will either return to (in the Test Font window) how they should be, or change into something else.. It’s really odd and I don’t know why it would be doing it.. Ideas?

If you send me the font, I might be able to figure out what you’re talking about. To which characters are you mapping these new glyphs?