Adding into Cookie's post above, as far as I know, it can be both a glitch or an actual indication that there are spaces present. The two things that I've found to work were using the arrow keys to shift your curser along the name and see if there was a space (then back spacing) to both the front and the end of the name, or to edit your character bit-by-bit, saving as you go (so as not to lose progress). If you have been typing in the same name for all three characters, perhaps try a different name (make sure you aren't typing in any oddd symbols like "*", as this can cause trouble, for some)!
Hopefully this helps. c: