The screenshot you took, I don't have that markup. Haven't for a long time.
Oh geez. I think I've found the bug for why it doesn't show up for me. Hopefully when I fix it it will also fix it for you : /
Okay, I think I fixed it, tell me what you see.
Nope. Let me know if you want screenshots. Basically, I have the markup button when I'm replying to comments, or to notifications, but not when I reply to the main post. Absolutely no idea why. EDIT: also when I'm on notifications page and I hit 'parent', the reply box that pops up is missing the markup button. (This is separate from the box that appears when I just hit 'reply' -- that one's fine.)
Ya, if you could screenshot it that'd be awesome. At this point I'm looking for a mess-with-flagamuffin function hidden somewhere in the code.