Add more standing animation sprites, that would be my suggestion. If this is your first character, I'm guessing you're editing a KFM.sff file? If not, you should start there, after all, that's all the first creators had to start with, except Elecbyte lol. Just try to copy that, or another file, as close as possible, and it should solve it.

If that isn't the case, then your animations don't match the sprite. Don't know what I mean? Try and copy a character's .sff into another character's file, and change the .def of that character to include the new .sff instead. When you load the character, there will be some animations where the character goes invisible.

This tells me that either your sprites aren't matching what the other documents tell it to, or there simply aren't enough sprites to allow the animation.

Give that a shot, hopefully it helps/solves things for you.