We have recently upgraded from 2011 to 2013 and are seeing a very strange scenario on the content delivery side. The dynamic component presentations are being returned to the webpage seemingly as Unicode Han Characters (搼癩椠㵤昢 etc), even though in the database I can see the valid html.
When using the jsp tag lib (tridion:ComponentPresentation) or java code (ComponentPresentationAssembler) we experience the issue, however using the content delivery webservice it is return correctly.
For background the publishing target is configured as JSP / Unicode (UTF-8), and the JSP page has pageEncoding set to utf-8.
Any ideas would be greatly appreciated.