The InsertHTML command moves elements around in the DOM and produces extra span elements each time it's executed.
Steps to reproduce:
1. Open the attached URL.
2. Place caret inside editable strong element below.
3. Click the InsertHTML link.
4. Observe that a new span element is added each time you click the InsertHTML button.
6627 depends on this bug not the other way around. Fixing.
This bug doesn't reproduce for me anymore. It has probably been solved by now.