Rich text fields, field locking, and form saving/re-opening

I have a LiveCycle form that has 2 text fields (email and info) and a button. When the button is pressed, the 2 text fields are set readonly and the button is set hidden. A rich text field is populated to provide a mailto link using the email and info text fields:

form1.firstpage.HyperlinkSF.rtField.value.exData.loadXML(sRichText, false, true);

This appears to work fine, but when I save the form and re-open it, the readonly fields are now editable and the button has re-appeared. If I remove the functionality associated with the rich text hyperlink, the form correctly re-opens with the readonly fields set readonly and the button is not visible.

Any idea why populating a rich text field is affecting the form state on saving/re-opening?