Umbraco doctype - rich text editor field keeps converting back to Textstring

In Umbraco I have a property of type textstring for a property on a doctype. I change the data type to rich text editor. Initially it works, however after a while it switches back to textstring. Is there a known fix for this?

Edit - I'm on Umbraco 4.7.1.1

Dirk De Grave implies that the issue may be to do with the Texdata having been stored in the dataNtext column in the cmsPropertyData:

http://our.umbraco.org/forum/templating/templates-and-document-types/26693-Safely-change-property-type-from-Textstring-to-Richtext-editor

... so copying all the data into the dataNvarchar column of the cmsPropertyData table for the affected documents may work, however I really shouldn't need to be doing this.

I'm thinking of adding a new property to my doctype, set up as richtexteditor from the outset, and re-entering the text, however if this works it's only a workaround, not a solution


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/44893-umbraco-doctype-rich-text-editor-field-keeps-converting-back-to-textstring