I see you don't have a HDCP issue (I never run protected content so don't really think about it)
Unfortunately, it is not always a factor of the content but sometimes of the hardware. Some devices like the Mac mini apparently enable HDCP whenever they see they are connected to a HDCP compliant device rather than only when the content calls for it. Because HDCP is then enabled, if you have something not HDCP compliant after that such as an HDMI-to-HD-SDI converter, CODEC, etc. then those devices can't receive any HD signals. The newer Matrox DualHead2Go Digital ME and Digital SE versions are HDCP compliant thus they could trigger such a response from some sources.
This has gotten to be such a common issue that AMX, Cretsron and others making digital media routers have included the option to turn off HDCP for individual inputs. It means those inputs cannot accept HDCP encrypted content but it also means they will not trigger the source device to enable HDCP.