Consider the following scenario: You are having a conversation with someone and you find an interesting piece from an article you come across on the internet. You select one or two paragraphs, copy it and then paste it into the message window, you'll notice that the input box resizes itself (presumably to let you see what's just been pasted in), and then hit Enter/Return. Instead of the input box being resized to its previous state, it stays in the larger state.
Full reproduction steps:
1. Launch Adium 1.2.3.
2. Open a message window with a contact.
3. Navigate to a website or copy a large chunk of text into the input box in Adium, and then press Return on the keyboard.
4. Note that the size of the message input box has not changed.
Version: 1.2.3, Mac OS X 10.5.2 on a MacBook Pro 15" 2.2 GHz. Screenshots are attached of before, before-paste, and after-paste results.