After updating to LiveCycle Designer ES2 QF4 (126.96.36.199.20110401.1.827986), you may notice that you are no longer able to delete the default value in rich-text fields. It is possible to edit the value, but when you delete it, the value will re-appear in the field after refreshing. This only happens for rich-text fields and not standard text fields.
This is an issue in LiveCycle Designer 9.5 QF4 and has been addressed in later versions, including Designer 10. If you require a quickfix for this issue in LiveCycle Designer 9 you should contact the enterprise support team.
You can delete the default value by opening the XML Source tab and removing the value manually.