There's that really helpful visual thing when you post AGS code into forum posts.
I used the Code Button to share code in my reply. All great.
Then I saw a typo and clicked on the "Quick edit" button.
And, visually, the code part wasn't there anymore like it's supposed to be (that dark visual)
So I clicked on "More > Modify" and then it wall alright again.
Cheers :)
I have a vague memories of reporting this a while ago.
It works after you refresh a page.
The code highlighting is a client-side script probably that runs after the page has loaded. The preview mechanism doesn't refresh the page though, it just fetches the post contents and updates it live on the page. The fix is to manually run the code script again. Probably a simple fix if you know where to look.