Is there some list of reserved system properties?

If I define global property ${endpoint} and insert it into endpoint field, then it doesn't work in test cases (but works in requests). In error log it gives following error:

ERROR:com.eviware.soapui.model.iface.Request$SubmitException: com.eviware.soapui.impl.wsdl.submit.RequestTransportRegistry$MissingTransportException: Missing protocol in endpoint [${endpoint}]

If I rename this global property, then test case is working.

I assume there is some list of reserved system properties? Can I see somewhere this list?