New lines inserted after header containers are broken in Chrome/Safari

Steps to reproduce:

1. Visit the demo page in Chrome 19 or Safari 5.1.7 - http://files.wymeditor.org/wymeditor/examples/01-basic.html
2. Change the 'Hello World' paragraph container to any header container
3. Place the cursor at the end of the 'Hello World' text and hit enter

Expected result: a new paragraph container is created below the header container. This occurs in Firefox.

Actual result: a plain div is created below the header container. This div container cannot be changed to any other type of container. The only way to fix this is to switch to HTML view and change the div to another standard container (ex. p or h1).