Yes, its vBulletin functionality, but i don't see its a BUG, its just a requirement to change the way the way it works.

We've been using vBulletin for many years now, nothing has changed to my knowledge.

I use the preview, yes, but this issue has not affected my posts since they are mainly text.

I know that the editor can produce some strange results when you try to hard format text in articles. But i work around it.

I'll drill through the bug reports and development requests on the vbulletin support site to see if there is any other mention of this or a proposed solution.

It maybe that there is some way to use a different editor. In Joomla we can install enhanced editors to resolve issues, but in VBulletin i've not seen this.