How to repeat: Go to the RHQ Server resource, Monitor tab. Click "Advanced Settings" for the metric range. set "From" to tomorrow's date, "To" to yesterday's date. Click OK. Note the message "Preferences updated Your preferences have been successfully updated". But when you click close, it's still in "Simple Mode".
RHQ-1711 resolved this indirectly.
This bug was previously known as http://jira.rhq-project.org/browse/RHQ-1478