You can enable language string debugging within CB > Configuration > Integrations. It's likely though that your string has extra tags surrounding it or if you have multiple languages for Joomla/CB then you maybe missing a language plugin for the language currently being used.
(By the way could you add a setting to choose the default editor for cbsubs settings ? if we use the standard one we always have html tags when saving a plan whatever the settings for the editor.)
We'll probably eventually use our own internal WYSIWYG editor to avoid all these issues. Until then you can use the Source view of your editor (every editor should have this as a button somewhere) or edit your editors settings in Extension > Plug-in Manager and set new line element to br instead of p, which typically should fix this.