The problem doesn't seem to occur with edits using the Wiki Markup or when we use another browser, like Firefox.

Here's how to reproduce the problem:
1. In IE7, create a new test page and add two new headers. Save them.
Example:

h4. Test 1

h4. Test 2

2. Re-edit the page in the Rich Text editor. Try added some text under the first header and hit Save. Your edits are gone. You can also see the behavior if you make these same edits in the Rich Text editor and then switch to Wiki Markup. The edits are gone again.