Any page with a Java addin - for example - I use the built-in Tabs. After I install any of your adding, I can no longer use the DW interface. A Big blue "B" is in the lower left corner of the "Properties" panel. Along the bottom is a link: "Download the web's best dreamweaver extentions...."
Since I pay for the products and there's not a SINGLE DMX feature on this page, I can't understand why I have to see a DMX ad, and why there's a DMX addin interfering with the editing of the page.
The issue you are having is caused by the fact that you are using a div with class "container". The class "container" is being used in the Bootstrap Framework, and the "B" that is displayed is there as you have the Free Bootstrap Extension installed in your Dreamweaver. Dreamweaver sees the class "container" and shows the Bootstrap Properties in the Properties Inspector. You can either change the class on your page or just temporary disable the Bootstrap extension.