Caret is lost when applying heading style on empty body

Follow this steps to reproduce on Firefox 9.0.1:

1. edit a new page (the content must be empty)
2. apply "Title 1" heading style
3. type some text

The caret is lost after step 2 so step 3 has no effect. Note that the caret is not hidden, it is really lost because the tool bar features become disabled.