1. Open the Page Editor->Header tab. Click New Header and enter:

 <script type="text/javascript"
</script> 

Click OK to save the header.

2. Open the Page Editor->Header tab and, when the custom header is highlighted, press the "a" key. As expected, the entire contents of the header is replaced with the letter "a". Now click the Cancel button so this change does not stick.

3. Open the Page Editor->Header tab and observe the header contents now contains the letter "a", which we had cancelled.

OK, have passed this on to QA.