Ooh, this can be frustrating.
Do as Enoki and Preach suggested, but also keep in mind that there is a limit to how much you can write in a bio.
Also, do you mean that it disappears from your character's bio, or from a group bio you are trying to create?
Group bios will show what you type, even when you've gone past the limit, but once you exit out from writing it, all your work up until the limit will disappear.
If this is the case, it's best to exit out of the group bio maker every now and then when writing it, just to make sure everything is staying there.
