I'm messing around with the editor, to get an idea of where to add a new button, and I click one of the buttons. It get's highlighted like it normally would, but when you click [close tags] instead of clicking on it again, it inserts the end code, but doesn't un-highlight the button that I click on. The only way to un-highlight the button after you click [close tags] is to click on it to add the tag, then click on it again to add the closing tag.
Please do not PM me about problems you might be having with MyBB. Post a thread, and someone on the support or development team will take a look at it.