So, it's responding like you've clicked the Post button?
As in, you're typing away like and you hit Enter, say you want to start a new paragraph, but rather than a new line appearing it's like you've clicked the Post button next to the Colour drop down / at the bottom of the field?
Does the problem manifest itself if you type a single line post and click the Post button without pressing Enter?
And, are you using TinyMCE (WYSIWYG HTML toolbar) or the built-in Beehive Simple HTML toolbar?
It happens when I hit the post button.
It happens whether I've typed a single line and attempted to post or typed several paragraphs and attempted to post. The message text entry window clears and the error message is displayed.
It isn't happening in response to the enter/carriage return button on the keyboard - only the post button.
It's the WYSIWYG toolbar.
Assuming this post works then it isn't happening when I use Firefox.
Switch back to The Simple HTML toolbar, reload the post page and then revert back to the WYSIWYG toolbar and see if that helps.
Otherwise it seems there is a bug in TinyMCE somewhere or BH's implementation of it, but I wouldn't have a clue where.