There was an .xml displaying after every post, but I came across solution to avoid that while re-adding it to Opera 10.
Right click in text box at Twitter - Create Search...
Pick a keyword
Expand Details --> and check if Use POST is selected.
I personally rather use Twitter Opera widget, but custom search comes in handy when you want to post a piece of text. All you need to do is select text, right click, search with, Twitter.
Note: Might only work in Opera you've created search in and not when synchronized to another Opera using Opera Link.