That's really a problem of the editor. But the editor before in the green forum also had some problems. Therefore I wrote all my stories in word and than put the whole text in the Forum editor to save it. After that step, i've done the pictures. May be that would bei more sure for your story.
I started doing the same thing. I think the chapter is actually coming along better now! It was a shame to lose so much progress, but I think I found a better direction to go in.
I'm gonna take it as something that was meant to be. It starts to act up after a couple hours of writing.
