Oy, I just had a heck of a time with a post I just made. Everything looked great in the preview, and I mostly use html when I format, but I hadn't put the html tags at the start and end of my post.

When I published it a whole section ended up being pushed right, despite closing the command with an end tag. I think I know what @jonknight is talking about with his center tag not closing. Steemit doesn't like if you try to mix match html in a markdown post I guess, even though the preview will make you think all's well.

Going back to edit is a pain, then I have to add paragraph tags because adding the html tag blew all that away. Eh. Then fun in learning, right? For me, I just need to remember to go full html every time. There's just enough format options unavailable with markdown that makes me not switch over.

Ooooh man, then I go to edit the post to fix it after adding html tags... yeah, more mess. It shows markdown (I think) in the edit window, then if you click to view raw html, half of my html tags are missing, screwing up the formatting of my post.
MORAL OF THE STORY: When you publish, it better be all markdown or all html from the get go!