Why is it when I'm using the advanced option (or tweaking my signature) that when i make a typo and press the delete button the curser resets to the beginning of the sentence and starts deleting stuff i didnt ask it to delete?

This is particularly a problem when I'm tweaking my signature cos it ends up taking the last ] away from my sig pic and if i dont check it im bothered because im getting coding on my sig instead of a picture.

Ive noticed this any time ive used the advanced option, i suspect it has something to do with the auto save feature but im not sure.

Is there a fix for this? It would help me as I'm a bit of a Typo Queen (as well as being a stubborn Retro Queen)