For best results when editing a post you've already made on the forum:
After clicking on "Edit" at the bottom of your post, click on "Use Full Editor".
Then after making your changes, before clicking on "Submit Modified Post", click on "Preview Post" to see how it will look and make sure it looks the way you expect.
If the Preview looks the way you want it to, then click on "Submit Modified Post". If it's way screwed up and you just want to start over, click on Cancel.
This approach is an especially good practice whenever you reply to a post by "Quote"-ing the post. The quoted post can get screwed up in the post quoting it, but "Use Full Editor" for some reason usually avoids that. And Use Full Editor allows you to Preview Post so you know how it's going to look.
