This is a bug. We are planning to patch it this evening. Check back in the am..should be fixed then.
Sorry for the trouble -
Take a look at the following article:
Change style—ArcGIS Online Help | ArcGIS
Do you see this change style image?
Click it to change the style of your layers.
This is only related to Map notes, not embedded layers - those can be changed.
To change the symbology with map notes, Click on the point> and the edit link in the pop up and then click the change symbol option.
Retrieving data ...