Firefox 2.0:
Here's the closest I can get to reproducing it:
* Paste some text directly into the editor. Sometimes it will break it up directly into paragraphs, sometimes it wont. Often, some of it will be correctly in containers and a small part will not. (Example, try cutting and pasting the text in the following article into an editor: http://www.naw.org/Content/ContentGroups/News2/After_the_flood.htm
You will see that the Sources section at the bottom doesn't copy correctly...i.e. has no container)
* Eventually you will get some text that does not appear in a container.
* Now try to put this text into a container. The only way i've been able to do it is go to the end of the text, hit enter to get a new <p> and then copy the text without container into the new <p>. Sometimes this doesn't work.
Problem: I have not been able to figure out how to get a container around text that has none without cutting and pasting again into an existing one.