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?