I was just trying to reproduce the issue. Unsuccessfully. I made new blog entry, but didn't approve it just go to preview. On preview it was opaqued with lang bbcode what is expected. When I set preview again it was just fine at it should be. Maybe I'm trying to reproduce it in wrong way, or didn't understood the issue. I thought that the issue is about adding lang bbcode when it is already added. But I see no such behavior.

Please note that if you are writing message and want to preview it will be opaqued by lang bbcode according to chosen language detection strategy. This is as it suppose to work. And if you remove it and see preview again then it will again detect language and add lang bbcode. This is as it should be. Because preview does same things as submit, just withour saving it into database. So yo have to see exactly same thing which will be inserted into database when you submit it.

Please tell does the issue exists and I was checking it wrong, or it is as we designed it?