14 DAY TRIAL // It looks like working with the new TweetDeck in Opera is not exactly a smooth ride in some cases. The Norwegian developer has been getting reports that users are having trouble sending tweets, replying, re-tweeting or seeing what is trending.
However, the response from Opera was swift and they delivered an easy fix for the situation. Simply check if there are new updates for the browser, even if you know for sure that you have the latest version. Hit the OK button when you receive the message that the application is up-to-date and the fix, an updated browser JS file, should already be implemented.
In the final step, you should reload Twitter. A browser restart may be required if the issues still persist. You can check if the fix has been implemented on this page where it should say "Opera Desktop 12.00 core 2.10.289, July 17, 2012. Active patches: 218".