I'm running OpenMRS 1.6.2 and XForms 188.8.131.52 (though I've had this problem with previous versions of XForms as well). What I find is that if I do several changes in the properties of concepts and then I hit save, and the either close the xforms or go to preview it, those changes aren't saved. This seems to happen somewhat randomly and from what I can tell only with the changes done Properties tab of the concepts e.g. if the concept is Visible, Blocked, Required, or the default value.
Here's one scenario where it makes de error consistently in both Chrome and Firefox 12.0
Add a new concept to an existing form
go into the form, refresh to see the new concept, touch the concept and enter a value for default value
hit save button
What happens is that the designer closes the concept I just placed the default value for, highlights the name of the page of the form, says form saved successfully, but when I go to the concept, the default value is not there.