Editing a thread's original post changes it back to the state of the unedited version

Editing a thread's original post more than once is really annoying, as when you try to edit, the only text that really pops up is the text from the unedited version of the post, before you edited it the first time. I've lost entire sections from simply adding a single sentence to the OP, and had to backpedal or write them over again.

I assume this isn't intentional, but please fix it as it's not very fun to deal with.